Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2015	Feb. 15, 2016	Jun. 30, 2015
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY
Trading Symbol	MACK
Entity Registrant Name	MERRIMACK PHARMACEUTICALS INC
Entity Central Index Key	0001274792
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		116,060,572
Entity Public Float			$ 1,286,139,750

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 185,606	$ 35,688
Marketable securities		88,340
Restricted cash	101	101
Accounts receivable, net	6,483	3,313
Inventory	3,717
Prepaid expenses and other current assets	5,487	4,623
Total current assets	201,394	132,065
Restricted cash	584	584
Property and equipment, net	21,915	14,502
Other assets	27	25
Intangible assets, net	7,355	7,725
Goodwill	3,605	3,605
Total assets	234,880	158,506
Current liabilities:
Accounts payable, accrued expenses and other	52,082	37,236
Deferred revenues	50,137	59,275
Deferred rent	1,527	1,285
Long-term debt, current portion		13,315
Total current liabilities	103,746	111,111
Deferred revenues, net of current portion	51,197	35,682
Deferred rent, net of current portion	4,926	5,401
Deferred tax incentives, net of current portion	1,045	496
Long-term debt, net of current portion	257,655	106,687
Accrued interest		1,200
Total liabilities	$ 418,569	$ 260,577
Commitments and contingencies
Non-controlling interest	$ 239	$ 69
Stockholders' deficit:
Preferred stock, $0.01 par value: 10,000 shares authorized at December 31, 2015 and 2014; no shares issued or outstanding at December 31, 2015 or 2014
Common stock, $0.01 par value: 200,000 shares authorized at December 31, 2015 and 2014, 115,871 and 106,697 issued and outstanding at December 31, 2015 and 2014, respectively	$ 1,159	$ 1,067
Additional paid-in capital	617,145	552,037
Accumulated other comprehensive loss		(74)
Accumulated deficit	(802,232)	(655,170)
Total stockholders' deficit	(183,928)	(102,140)
Total liabilities, non-controlling interest and stockholders' deficit	$ 234,880	$ 158,506

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	115,871,000	106,697,000
Common stock, shares outstanding	115,871,000	106,697,000

Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues:
Product revenues, net	$ 4,328	$ 0	$ 0
License and collaboration revenues	84,930	102,756	47,786
Total revenues	89,258	102,756	47,786
Costs and expenses:
Cost of product revenues	46	0	0
Research and development expenses	160,988	138,495	147,139
Selling, general and administrative expenses	57,795	30,517	21,187
Total costs and expenses	218,829	169,012	168,326
Loss from operations	(129,571)	(66,256)	(120,540)
Other income and expenses
Interest income	99	114	166
Interest expense	(19,232)	(18,230)	(10,938)
Other income, net	917	813	627
Net loss	(147,787)	(83,559)	(130,685)
Less net income (loss) attributable to non-controlling interest	170	(268)	240
Net loss attributable to Merrimack Pharmaceuticals, Inc.	(147,957)	(83,291)	(130,925)
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities	74	(50)	14
Other comprehensive income (loss)	74	(50)	14
Comprehensive loss	$ (147,883)	$ (83,341)	$ (130,911)
Net loss per share available to common stockholders-basic and diluted	$ (1.33)	$ (0.80)	$ (1.32)
Weighted-average common shares used in computing net loss per share available to common stockholders-basic and diluted	111,356	104,410	98,919

Consolidated Statements of Non-Controlling Interest and Stockholders' Deficit - USD ($) shares in Thousands, $ in Thousands	Total	Silver Creek Series B Preferred Stock [Member]	Non-controlling Interest [Member]	Non-controlling Interest [Member] Silver Creek Series B Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Silver Creek Series B Preferred Stock [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2012	$ (6,517)		$ 97		$ 958	$ 434,679		$ (38)	$ (442,116)
Balance (in shares) at Dec. 31, 2012					95,825
Exercise of stock options and common stock warrants	2,036				$ 9	2,027
Exercise of stock options and common stock warrants (shares)					948
Stock-based compensation	10,733					10,733
Issuance of common stock in a public offering, net of issuance costs	26,716				$ 58	26,658
Issuance of common stock in a public offering, net of issuance costs (shares)					5,750
Conversion option of convertible senior notes	51,875					51,875
Conversion of Silver Creek Pharmaceuticals, Inc. convertible notes payable	$ 1,807		796			$ 1,807
Conversion of Silver Creek Pharmaceuticals, Inc. convertible notes payable (shares)	0				0	0		0	0
Other comprehensive income	$ 14							$ 14
Loss attributable to non-controlling interest	556		(556)						$ 556
Net loss	(130,685)								(130,685)
Balance at Dec. 31, 2013	$ (43,465)		337		$ 1,025	$ 527,779		$ (24)	$ (572,245)
Balance (in shares) at Dec. 31, 2013					102,523
Conversion option of convertible senior notes (shares)	0				0	0		0	0
Exercise of stock options and common stock warrants	$ 10,425				$ 42	$ 10,383
Exercise of stock options and common stock warrants (shares)					4,174
Stock-based compensation	13,197					13,197
Conversion of Silver Creek Pharmaceuticals, Inc. convertible notes payable	$ 678		366			$ 678
Conversion of Silver Creek Pharmaceuticals, Inc. convertible notes payable (shares)	0				0	0		0	0
Other comprehensive income	$ (50)							$ (50)
Loss attributable to non-controlling interest	634		(634)						$ 634
Net loss	(83,559)								(83,559)
Balance at Dec. 31, 2014	(102,140)		69		$ 1,067	$ 552,037		(74)	(655,170)
Balance (in shares) at Dec. 31, 2014					106,697
Exercise of stock options and common stock warrants	10,101				$ 54	10,047
Exercise of stock options and common stock warrants (shares)					5,360
Stock-based compensation	15,351					15,351
Issuance of common stock in a public offering, net of issuance costs	38,560				$ 38	38,522
Issuance of common stock in a public offering, net of issuance costs (shares)					3,814
Other comprehensive income	74							$ 74
Loss attributable to non-controlling interest	725		(725)						725
Issuance of preferred stock by Silver Creek Pharmaceuticals, Inc.		$ 1,188		$ 895			$ 1,188
Net loss	(147,787)								(147,787)
Balance at Dec. 31, 2015	$ (183,928)		$ 239		$ 1,159	$ 617,145			$ (802,232)
Balance (in shares) at Dec. 31, 2015					115,871

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities
Net loss	$ (147,787)	$ (83,559)	$ (130,685)
Adjustments to reconcile net loss to net cash used in operating activities
Non-cash interest expense	8,217	8,511	4,548
Depreciation and amortization	4,288	3,223	2,589
Stock-based compensation	15,351	13,197	10,733
Purchased premiums and interest on marketable securities		858	(1,809)
Other non-cash items	4		579
Changes in operating assets and liabilities:
Accounts receivable	(3,170)	2,587	3,410
Prepaid expenses and other current assets	(850)	827	4,037
Inventory	(3,717)
Accounts payable, accrued expenses and other	13,557	(646)	13,304
Deferred revenues	6,377	19,482	(4,989)
Deferred rent and tax incentives	2,374	712	2,076
Other assets and liabilities, net			1,032
Net cash (used in) operating activities	(105,356)	(34,808)	(95,175)
Cash flows from investing activities
Purchase of marketable securities		(111,832)	(112,923)
Proceeds from sales and maturities of marketable securities	87,899	111,858	95,100
Purchase of property and equipment	(12,789)	(6,035)	(9,857)
Assignment of restricted cash			(57)
Other investing activities, net		(2)	(2)
Net cash provided by (used in) investing activities	75,110	(6,011)	(27,739)
Cash flows from financing activities
Proceeds from public offerings, net of issuance costs	38,560		26,716
Proceeds from exercise of options and warrants to purchase common stock	10,087	10,384	2,036
Proceeds from issuance of senior secured notes due 2022, net of issuance costs	169,434
Proceeds from issuance of preferred stock by Silver Creek Pharmaceuticals, Inc.	2,083
Proceeds from convertible notes issued by Silver Creek Pharmaceuticals, Inc., net of issuance costs		1,044	121,537
Repayment of loans payable to Hercules Technology Growth Capital, Inc.	(40,000)
Payments of dividends on Series B convertible preferred stock		(7)	(3)
Net cash provided by financing activities	180,164	11,421	150,286
Net increase (decrease) in cash and cash equivalents	149,918	(29,398)	27,372
Cash and cash equivalents, beginning of period	35,688	65,086	37,714
Cash and cash equivalents, end of period	185,606	35,688	65,086
Non-cash investing and financing activities
Issuance of derivative liability			35
Value of conversion feature of convertible senior notes, classified in Stockholders' Deficit			51,876
Property, plant and equipment in accounts payable and accrued expenses	816	704
Receivables related to stock option exercises in prepaid expenses and other current assets	14
Disposals of fully-depreciated property and equipment	303	1,603	210
Reclassification of deferred financing costs to stockholders' deficit			278
Conversion of Silver Creek Pharmaceuticals, Inc. convertible notes		1,044	2,603
Supplemental disclosure of cash flows
Cash paid for interest	$ 10,087	$ 9,510	$ 3,915

Nature of the Business and Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2015

Accounting Policies [Abstract]

Nature of the Business and Summary of Significant Accounting Policies

1. Nature of the Business and Summary of Significant Accounting Policies

Nature of the Business

Merrimack Pharmaceuticals, Inc. (the “Company”) is a biopharmaceutical company discovering, developing and commercializing innovative medicines consisting of novel therapeutics paired with diagnostics for the treatment of cancer. The Company has one marketed therapeutic oncology product and multiple targeted therapeutic oncology candidates in clinical development. The Company’s most advanced program is its therapeutic MM-398, which the Company markets in the United States under the brand name ONIVYDE. In addition to ONIVYDE and its product candidates in clinical development, the Company has multiple product candidates in preclinical development and a discovery effort advancing additional candidate medicines. The Company has tailored ONIVYDE and its other product candidates to target specific disease mechanisms that its research suggests are common across many solid tumor types. The Company believes that ONIVYDE and its other product candidates have the potential to address major unmet medical needs. The Company also has an agreement to utilize its manufacturing expertise to develop, manufacture and exclusively supply bulk drug product to a third party, who will in turn process the drug into a finished product and commercialize it globally following regulatory approval. The Company was incorporated in the Commonwealth of Massachusetts in 1993 and reincorporated in the State of Delaware in October 2010.

The Company is subject to risks and uncertainties common to companies in the biopharmaceutical industry, including, among other things, its ability to secure additional capital to fund operations, success of clinical trials, development by competitors of new technological innovations, dependence on collaborative arrangements, protection of proprietary technology, compliance with government regulations and dependence on key personnel. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel, infrastructure and extensive compliance reporting capabilities.

The Company has incurred significant losses and has not generated significant revenue from commercial sales. The accompanying consolidated financial statements have been prepared on a basis which assumes that the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the normal course of business.

The Company may seek additional funding through public or private debt or equity financings, or through existing or new collaboration arrangements. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into additional collaborative arrangements. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. Arrangements with collaborators or others may require the Company to relinquish rights to certain of its technologies or product candidates. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate its research and development programs or commercialization efforts, which could adversely affect its business prospects.

Summary of Significant Accounting Policies

Segment Information

Operating segments are defined as components of an enterprise engaging in business activities for which discrete financial information is available and regularly reviewed by the chief operating decision maker in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment and the Company operates in only one geographic region.

Basis of Presentation and Consolidation

The accompanying consolidated financial statements have been prepared under U.S. generally accepted accounting principles (“GAAP”) and include the accounts of the Company and its wholly owned subsidiary, Merrimack Pharmaceuticals (Bermuda) Ltd., which was merged with and into the Company during the third quarter of 2014. The Company also consolidates its majority owned subsidiary, Silver Creek Pharmaceuticals, Inc. (“Silver Creek”). All intercompany transactions and balances have been eliminated in consolidation.

Use of Estimates

GAAP requires the Company’s management to make estimates and judgments that may affect the reported amounts of assets, liabilities, revenues, expenses and related disclosures. The Company bases estimates and judgments on historical experience and on various other factors that it believes to be reasonable under the circumstances. The most significant estimates in these consolidated financial statements include, but may not be limited to, revenue recognition, including the estimated percentage of billable expenses in any particular budget period, periods of meaningful use of licensed products, estimated service periods and services to be completed under a collaboration, estimates used in accounting for revenue separability and recognition, estimates of discounts and allowances related to commercial sales of ONIVYDE, estimates utilized in the valuation of inventory, useful lives with respect to long-lived assets and intangible assets, accounting for stock-based compensation, contingencies, intangible assets, goodwill, in-process research and development, tax valuation reserves and accrued expenses. The Company’s actual results may differ from these estimates under different assumptions or conditions. The Company evaluates its estimates on an ongoing basis. Changes in estimates are reflected in reported results in the period in which they become known by the Company’s management.

Cash, Cash Equivalents and Restricted Cash

Cash and cash equivalents are short-term, highly liquid investments with original maturities of three months or less at the date of purchase. Investments qualifying as cash equivalents primarily consist of money market funds, commercial paper, corporate notes and bonds and certificates of deposit.

Cash accounts with any type of restriction are classified as restricted cash. If restrictions are expected to be lifted in the next twelve months, the restricted cash account is classified as current. As of both December 31, 2015 and 2014, the Company recorded restricted cash of $685,000, which was primarily related to the Company’s facility lease.

Marketable Securities

The Company classifies marketable securities with a remaining maturity when purchased of greater than three months as available-for-sale. Available-for-sale securities may consist of U.S. government agencies securities, commercial paper, corporate notes and bonds and certificates of deposit, which are maintained by an investment manager. Available-for-sale securities are carried at fair value, with the unrealized gains and losses included in other comprehensive income (loss) as a component of stockholders’ deficit until realized. To determine whether an other-than-temporary impairment exists, the Company performs an analysis to assess whether it intends to sell, or whether it would more likely than not be required to sell, the security before the expected recovery of the amortized cost basis. Where the Company intends to sell a security, or may be required to do so, the security’s decline in fair value is deemed to be other-than-temporary and the full amount of the unrealized loss is recognized on the statement of operations and comprehensive loss as an other-than-temporary impairment charge. When this is not the case, the Company performs additional analysis on all securities with unrealized losses to evaluate losses associated with the creditworthiness of the security. Credit losses are identified where the Company does not expect to receive cash flows, based on using a single best estimate, sufficient to recover the amortized cost basis of a security and amount of the loss recognized in other income (expense). Realized gains and losses are recognized in interest income. Any premium or discount arising at purchase is amortized and/or accreted to interest income.

Inventory

The Company values its inventories at the lower of cost or net realizable value. The Company determines the cost of its inventories, which includes amounts related to materials and manufacturing overhead, on a first-in, first-out basis. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and it writes down any excess and obsolete inventories to their realizable value in the period in which the impairment is first identified. Such impairment charges, should they occur, are recorded within cost of product revenues.

The Company capitalizes inventory costs associated with the Company’s products after regulatory approval when, based on management’s judgment, future commercialization is considered probable and the future economic benefit is expected to be realized. Inventory acquired prior to receipt of marketing approval of a product candidate is expensed as research and development expense as incurred. Inventory that can be used in either the production of clinical or commercial product is expensed as research and development expense when selected for use in a clinical manufacturing campaign.

Shipping and handling costs for product shipments are recorded as incurred in cost of product revenues along with costs associated with manufacturing the product and any inventory reserves or write-downs.

Property and Equipment

Property and equipment, including leasehold improvements, are recorded at cost and depreciated when placed into service using the straight-line method, based on their estimated useful lives as follows:


Asset classification		Estimated useful life (in years)
Lab equipment		3 - 7
IT equipment		3 - 7
Leaseholds improvements		Lesser of useful life or lease term
Furniture and fixtures		3 - 7

Costs for capital assets not yet placed into service have been capitalized as construction-in-progress and will be depreciated in accordance with the above guidelines once placed into service. Costs for repairs and maintenance are expensed as incurred, while major betterments are capitalized. The Company capitalizes interest cost incurred on funds used to construct property and equipment. The capitalized interest is recorded as part of the asset to which it relates and is depreciated over the asset’s estimated useful life. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is reflected in earnings.

The Company reviews its long-lived assets for impairment whenever events or changes in business circumstances indicate that the carrying amount of assets may not be fully recoverable or that the useful lives of these assets are no longer appropriate. Each impairment test is based on a comparison of the undiscounted cash flow to the recorded value of the asset. If impairment is indicated, the asset will be written down to its estimated fair value on a discounted cash flow basis.

Goodwill and Intangible Assets

Goodwill and indefinite-lived intangible assets, including in-process research and development (“IPR&D”), are evaluated for impairment on an annual basis or more frequently if an indicator of impairment is present. No impairment of goodwill resulted from the Company’s most recent evaluation, which occurred in the third quarter of 2015. The Company’s next annual impairment evaluation will be made in the third quarter of 2016 unless indicators arise that would require the Company to evaluate at an earlier date.

When performing an evaluation of goodwill impairment, the Company has the option to first assess qualitative factors to determine whether it is necessary to perform the quantitative two-step impairment test. If the Company elects this option and finds, as a result of the qualitative assessment, that it is more likely than not that the fair value of the reporting unit is less than its carrying amount, the quantitative two-step impairment test is required; otherwise, further testing is not required. This requires the Company to assess the impact of significant events, milestones and changes to expectations and activities that may have occurred since the last impairment evaluation. Significant changes to these estimates, judgments and assumptions could materially change the outcome of the impairment assessment. Alternatively, the Company may elect to not first assess qualitative factors and immediately perform the quantitative two-step impairment test. If such an election occurs, in the first step, the fair value of the Company’s reporting unit is compared to the carrying value. If the carrying value of the net assets assigned to the reporting unit exceeds the fair value of the reporting unit, then the second step of the impairment test is performed in order to determine the implied fair value of the reporting unit’s goodwill. If the carrying value of the reporting unit’s goodwill exceeds the implied fair value, then the Company would record an impairment loss equal to the difference. As described above, the Company operates in one operating segment, which is considered the only reporting unit.

The Company’s evaluation of IPR&D impairment in the third quarter of 2015 included a qualitative assessment to determine whether further impairment testing of indefinite-lived intangible assets was necessary. It was determined that it was not more likely than not that an impairment existed as of the third quarter of 2015 and, therefore, quantitative impairment evaluations were not performed.

The Company commences amortization of indefinite-lived intangible assets, such as IPR&D, once the associated research and development efforts have been completed and amortizes the assets over their estimated future lives. Definite-lived intangible assets, such as core technology and product-related intangibles, are evaluated for impairment whenever events or circumstances indicate that the carrying value may not be fully recoverable. Definite-lived intangible assets are separate from goodwill and indefinite-lived intangible assets and are deemed to have a definite life. The Company amortizes these assets over their estimated useful lives. The Company has not recorded any impairment charges related to definite-lived intangible assets during the years ended December 31, 2015, 2014 or 2013.

Accrued Expenses

As part of the process of preparing financial statements, the Company is required to estimate accrued expenses. This process involves identifying services that have been performed on the Company’s behalf and estimating the level of services performed and the associated costs incurred for such services where the Company has not yet been invoiced or otherwise notified of actual cost. The Company records these estimates in its consolidated financial statements as of each balance sheet date. Examples of estimated accrued expenses include:

•

fees due to contract research organizations in connection with preclinical and toxicology studies and clinical trials;

•

fees paid to investigative sites in connection with clinical trials; and

•

professional service fees.

In accruing service fees, the Company estimates the time period over which services will be provided and the level of effort in each period. If the actual timing of the provision of services or the level of effort varies from the estimate, the Company adjusts the accrual accordingly. In the event that the Company does not identify costs that have been incurred or it under or overestimates the level of services performed or the costs of such services, its actual expenses could differ from such estimates. The date on which some services commence, the level of services performed on or before a given date and the cost of such services are often subjective determinations. The Company prepares its estimates based on the facts and circumstances known to it at the time and in accordance with GAAP. There have been no material changes in estimates for the periods presented.

Non-Controlling Interest

Non-controlling interest represents the non-controlling stockholders’ proportionate share of preferred stock and net loss of the Company’s majority owned consolidated subsidiary, Silver Creek. The non-controlling stockholders’ proportionate share of the preferred stock in Silver Creek is reflected as non-controlling interest in the Company’s consolidated balance sheets as a component of mezzanine equity.

Revenue Recognition

The Company recognizes revenue when all of the following criteria are met: persuasive evidence of an arrangement exists; delivery has occurred or services have been rendered; the price to the customer is fixed or determinable; and collectability is reasonably assured.

Product Revenues, Net

The Company sells ONIVYDE to a limited number of specialty pharmaceutical distributors in the United States (collectively, its “Distributors”). The Company’s Distributors subsequently resell the products to healthcare providers. The Company recognizes revenue on product sales when title and risk of loss have passed to the Distributor, which is typically upon delivery. Product revenues are recorded net of applicable reserves for discounts and allowances.

In order to conclude that the price is fixed or determinable, the Company must be able to reasonably estimate its net product revenues upon delivery to its Distributors. As such, the Company estimates its net product revenues by deducting from its gross product revenues trade allowances, estimated contractual discounts, estimated Medicaid rebates, estimated reserves for product returns and estimated costs of other incentives offered to patients.

These discounts and allowances are based on estimates of the amounts earned or to be claimed on the related sales. The Company’s estimates take into consideration its historical experience, current contractual and statutory requirements, specific known market events and trends, industry data and forecasted Distributor buying and payment patterns. Actual amounts may ultimately differ from the Company’s estimates. If actual results vary, the Company will adjust these estimates, which could have an effect on earnings in the period of adjustment.

Product revenue reserves and allowances that reduce gross revenue are categorized as follows:

Trade Allowances: The Company pays fees to its Distributors for providing certain data to the Company as well as for maintaining contractual inventory and service levels. These trade allowances are recorded as a reduction to accounts receivable on the consolidated balance sheet at the time revenue is recognized.

Rebates and Chargeback Discounts: The Company is subject to discount obligations under state Medicaid programs and the Public Health Service 340B Drug Pricing Program, contracts with Federal government entities purchasing via the Federal Supply Schedule and various private organizations, such as group purchasing organizations (collectively, its “Third-party Payors”). The Company estimates the rebates and chargeback discounts it will provide to Third-party Payors, based upon its estimated payor mix, and deducts these estimated amounts from its gross product revenues at the time revenue is recognized. Chargeback discounts are processed when the Third-party Payor purchases the product at a discount from the Distributor, who then in turn charges back to the Company the difference between the price initially paid by the Distributor and the discounted price paid by the Third-party Payor. These chargeback discounts are recorded as a reduction to accounts receivable on the consolidated balance sheet at the time revenue is recognized. Rebates that are invoiced directly to the Company are recorded as accrued liabilities on the consolidated balance sheet at the time revenue is recognized.

Product Returns: An allowance for product returns is established for returns expected to be made by Distributors and is recorded at the time revenue is recognized, resulting in a reduction to product sales. In accordance with contractual terms, Distributors have the right to return unopened and undamaged product that is within a permissible number of months before and after the product’s expiration date, subject to contractual limitations. The Company has the ability to monitor inventory levels and the shelf life of product at Distributors and can contractually control the amount of inventory that is sold to Distributors. Based on inventory levels held by Distributors and the structure of the Company’s distribution model, the Company has concluded that it has the ability to reasonably estimate product returns at the time revenue is recognized. The Company’s estimated rate of return is based on historical rates of return for comparable oncology products.

Other Incentives: The Company offers co-pay mitigation support to commercially insured patients. The Company’s co-pay mitigation program is intended to reduce each participating patient’s portion of the financial responsibility for a product’s purchase price to a specified dollar amount. Based upon the terms of the Company’s co-pay mitigation program, the Company estimates average co-pay mitigation amounts in order to establish a reserve for co-pay mitigation claims and deducts these estimated amounts from its gross product revenues at the later of the date that (i) the revenues are recognized or (ii) the incentive is offered. Claims under the Company’s co-pay mitigation program are subject to expiration.

License and Collaboration Revenues

The Company enters into biopharmaceutical product development agreements with collaborative partners for the research and development of therapeutic and diagnostic products. The terms of the agreements may include nonrefundable signing and licensing fees, funding for research, development and manufacturing, milestone payments and royalties or profit-sharing on any product sales derived from collaborations. These multiple-element arrangements are analyzed to determine whether the deliverables can be separated or whether they must be accounted for as a single unit of accounting.

The revenue recognition guidance related to multiple-element arrangements requires entities to separate and allocate consideration in a multiple-element arrangement according to the relative selling price of each deliverable. The fair value of deliverables under the arrangement may be derived using a best estimate of selling price if vendor specific objective evidence and third-party evidence are not available. Deliverables under the arrangement will be separate units of accounting provided that a delivered item has value to the customer on a stand-alone basis and if the arrangement does not include a general right of return relative to the delivered item and delivery or performance of the undelivered item is considered probable and substantially in the control of the vendor.

The Company entered into a license and collaboration agreement with Baxter International Inc., Baxter Healthcare Corporation and Baxter Healthcare SA in September 2014, which was evaluated under the accounting guidance on revenue recognition for multiple-element arrangements. The Company determined that the obligations under this agreement represent a single unit of accounting and that the agreement represents a services agreement. As a result, the Company has estimated the level of effort expected to be completed as a result of providing the identified deliverables and will recognize revenue related to the agreement based on proportional performance as effort is completed over the expected services period.

The Company also entered into a collaboration agreement with Watson Laboratories, Inc. (“Actavis”) in November 2013, which was evaluated under the accounting guidance on revenue recognition for multiple-element arrangements. See Note 5, “License and Collaboration Agreements,” for additional information.

Whenever the Company determines that an arrangement should be accounted for as a single unit of accounting, it determines the period over which the performance obligations would be performed and revenue would be recognized. If the Company cannot reasonably estimate the timing and the level of effort to complete its performance obligations under the arrangement, then revenue under the arrangement is recognized on a straight-line basis over the period the Company expects to complete its performance obligations.

The Company’s collaboration agreements may include additional payments upon the achievement of performance-based milestones. As milestones are achieved, a portion of the milestone payment, equal to the percentage of the total time that the Company has performed the performance obligations to date divided by the total estimated time to complete the performance obligations, multiplied by the amount of the milestone payment, will be recognized as revenue upon achievement of such milestone. The remaining portion of the milestone will be recognized over the remaining performance period. Milestones that are tied to regulatory approvals are not considered probable of being achieved until such approval is received. Milestones tied to counterparty performance are not included in the Company’s revenue model until the performance conditions are met.

Royalty revenue will be recognized upon the sale of the related products provided the Company has no remaining performance obligations under the arrangement.

Research and Development Expenses

Research and development expenses are charged to expense as incurred. Research and development expenses comprise costs incurred in performing research and development activities, including personnel-related costs, stock-based compensation, facilities, research-related overhead, clinical trial costs, contracted services, research-related manufacturing, license fees and other external costs. The Company accounts for nonrefundable advance payments for goods and services that will be used in future research and development activities as expenses when the services have been performed or when the goods have been received rather than when the payment is made.

Advertising Expenses

In connection with the commercial launch of ONIVYDE on October 22, 2015, the Company began incurring advertising expenses. Advertising expenses are expensed as incurred. For the year ended December 31, 2015, advertising expenses totaled $1.0 million.

Stock-Based Compensation

Stock-based compensation expense related to employee stock options is measured using the fair value of the award at the grant date, net of estimated forfeitures, and is adjusted annually to reflect actual forfeitures. The fair value of each stock-based award is estimated using the Black-Scholes option valuation model, and stock-based compensation expense is recognized on a straight-line over the vesting period, which is also the requisite service period.

The Company records stock options issued to non-employees at fair value, remeasures to reflect the current fair value at each reporting period and recognizes expense over the related service period. When applicable, these equity instruments are accounted for based on the fair value of the consideration received or the fair value of the equity instrument issued, whichever is more reliably measurable.

Comprehensive Income (Loss)

Comprehensive income (loss) is defined as the change in equity of a business enterprise during a period from transactions, and other events and circumstances, from non-owner sources and currently consists of net loss and changes in unrealized gains and losses on available-for-sale securities.

Other Income and Expense

The Company records gains and losses on federal and state sponsored tax incentives and other income or expense-related items in other income and expense.

The Company has been awarded tax incentives by the Massachusetts Life Sciences Center (“MLSC”), an independent agency of the Commonwealth of Massachusetts. These tax incentives require that the Company achieve certain hiring targets. Failure to maintain the additional headcount in subsequent periods could require the Company to repay some or all of the incentives. The Company recognizes the benefit of these incentives on a straight-line basis over the five-year performance period of each award, beginning when the Company achieves the hiring goal target, with a cumulative catch-up recognized in the period that the hiring goal target is achieved. The Company has received MLSC tax incentives in 2011, 2013, 2014 and 2015 totaling $3.8 million in the aggregate, allowing the Company to monetize approximately $3.4 million of state research and development tax credits. The Company has recognized $0.7 million, $0.4 million and $0.3 million in income related to these tax incentives for the years ended December 31, 2015, 2014 and 2013, respectively.

Income Taxes

The Company accounts for income taxes under the asset and liability method. Under this method, deferred tax assets and liabilities are recognized for the estimated future tax consequences attributable to differences between financial statement carrying amounts of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted rates in effect for the year in which these temporary differences are expected to be recovered or settled. Valuation allowances are provided if based on the weight of available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized.

The Company provides reserves for potential payments of tax to various tax authorities related to uncertain tax positions and other issues. Reserves are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filing is more likely than not to be realized following resolution of any potential contingencies present related to the tax benefit. Potential interest and penalties associated with such uncertain tax positions are recorded as components of income tax expense. To date, the Company has not taken any uncertain tax positions or recorded any reserves, interest or penalties.

Concentration of Credit Risk

Financial instruments that subject the Company to credit risk consist primarily of cash and cash equivalents, marketable securities and accounts receivable. The Company places its cash deposits in accredited financial institutions and, therefore, the Company’s management believes these funds are subject to minimal credit risk. The Company invests cash equivalents and marketable securities in money market funds, U.S. government agencies securities and various corporate debt securities. Credit risk in these securities is reduced as a result of the Company’s investment policy to limit the amount invested in any one issue or any single issuer and to only invest in high credit quality securities. The Company has no significant off-balance sheet concentrations of credit risk such as foreign currency exchange contracts, option contracts or other hedging arrangements. The Company also is subject to credit risk from its accounts receivable related to its product sales and collaborators. The Company evaluates the creditworthiness of each of its customers and has determined that all of its customers are creditworthy. To date, the Company has not experienced significant losses with respect to the collection of its accounts receivable.

Gross revenues from each of the Company’s customers who individually accounted for 10% or more of total gross revenues for the years ended December 31, 2015, 2014 and 2013 consisted of the following:


	Years Ended December 31,
	2015	2014	2013
Baxalta	93%	10%	—
Sanofi	—	90%	98%

Gross accounts receivable related to each of the Company’s customers who individually accounted for 10% or more of total gross accounts receivable as of December 31, 2015 and 2014 consisted of the following:


	December 31,
	2015	2014
Baxalta	29%	49%
Sanofi	—	50%
AmerisourceBergen Corporation	29%	—
McKesson Corporation	25%	—
Cardinal Health, Inc.	16%	—

Recent Accounting Pronouncements

In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09, “Revenue from Contracts with Customers (Topic 606),” which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. This guidance was originally effective for interim and annual periods beginning after December 15, 2016 and allows for adoption using a full retrospective method, or a modified retrospective method. Early adoption was originally not permitted. In August 2015, the FASB issued ASU 2015-14, “Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date,” whereby the effective date for the new revenue standard was deferred by one year. As a result of ASU 2015-14, the new revenue standard is now effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2017, and early adoption is now permitted for annual periods beginning after December 15, 2016, including interim periods within that annual period. The Company is currently evaluating the potential impact that the adoption of this guidance and the related transition guidance may have on the consolidated financial statements, including the adoption method to be utilized.

In August 2014, the FASB issued ASU 2014-15, “Presentation of Financial Statements – Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern,” outlining management’s responsibility to perform interim and annual assessments of an entity’s ability to continue as a going concern within one year of the date the financial statements are issued and providing guidance on determining when and how to disclose going concern uncertainties in the financial statements. This guidance will be effective for annual and interim reporting periods ending after December 15, 2016, and early adoption is permitted. The Company does not anticipate a material impact to the consolidated financial statements as a result of this change.

In April 2015, the FASB issued ASU 2015-03, “Interest - Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs,” which requires that debt issuance costs related to a recognized debt liability be presented on the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. This update is effective for annual reporting periods beginning after December 15, 2015, including interim periods within those annual periods, and early adoption is permitted. Accordingly, the Company elected to early adopt ASU 2015-03 for the year ended December 31, 2015. As a result, less than $0.1 million of short-term debt issuance costs have been reclassified from “Prepaid expenses and other current assets” to “Long-term debt, current portion” and approximately $0.1 million of long-term debt issuance costs have been reclassified from “Other assets” to “Long-term debt, net of current portion” on the Company’s consolidated balance sheet as of December 31, 2014. This early adoption had no impact on the Company’s consolidated statements of operations and comprehensive loss for any period presented.

In July 2015, the FASB issued ASU 2015-11, “Inventory (Topic 330): Simplifying the Measurement of Inventory,” to simplify the subsequent measurement of inventory. Entities are now required to subsequently measure inventory at the lower of cost or net realizable value rather than at the lower of cost or market. This update is effective for annual reporting periods beginning after December 15, 2016, including interim periods within those annual periods, and early adoption is permitted. Accordingly, the Company elected to early adopt ASU 2015-11 for the year ended December 31, 2015. There was no impact to the consolidated financial statements as a result of this change.

In November 2015, the FASB issued ASU 2015-17, “Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes,” to simplify the presentation of deferred income taxes by requiring that deferred tax liabilities and assets be classified as noncurrent on the balance sheet. This update is effective for annual reporting periods beginning after December 31, 2016, including interim periods within those annual periods, and early adoption is permitted. Accordingly, the Company elected to early adopt ASU 2015-17 for the year ended December 31, 2015. There was no impact to the consolidated financial statements as a result of this change.

Marketable Securities

12 Months Ended

Dec. 31, 2015

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

2. Marketable Securities

As of December 31, 2015, the Company maintained no marketable securities. Marketable securities as of December 31, 2014 consisted of the following, all of which were classified as available-for-sale:


	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
December 31, 2014:
Commercial paper	$	6,493	$	—	$	(2	)	$	6,491
Corporate debt securities		81,921		—		(72	)		81,849

Total	$	88,414	$	—	$	(74	)	$	88,340

The aggregate fair value of securities held by the Company in an unrealized loss position for less than 12 months as of December 31, 2014 was $88.4 million, representing 35 securities. As of December 31, 2014, the Company did not intend to sell, and it was not more likely than not that the Company would be required to sell, the investments in an unrealized loss position before recovery of their amortized cost bases. The Company determined that there was no material change in the credit risk of the investments. As a result, the Company determined it did not hold any investments with an other-than-temporary-impairment as of December 31, 2014.

There were no realized gains or losses recognized on the sale or maturity of marketable securities during the years ended December 31, 2015, 2014 or 2013.

- Definition

The entire disclosure for investments in certain debt and equity securities.

+ References + Details

Net Loss Per Common Share

12 Months Ended

Dec. 31, 2015

Earnings Per Share [Abstract]

Net Loss Per Common Share

3. Net Loss Per Common Share

Basic net loss per share is calculated by dividing the net loss available to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is computed by dividing the net loss available to common stockholders by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method. For purposes of this calculation, convertible preferred stock, stock options and warrants are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive.

As discussed in Note 11, “Borrowings,” in July 2013, the Company issued $125.0 million aggregate principal amount of 4.50% convertible senior notes due 2020 (the “Convertible Notes”) in an underwritten public offering. Following the repayment and satisfaction in full of the Company’s obligations to Hercules Technology Growth Capital, Inc. (“Hercules”) under its Loan and Security Agreement with Hercules (the “Loan Agreement”), which occurred in December 2015, upon any conversion of the Convertible Notes, the Convertible Notes may be settled, at the Company’s election, in cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock. For purposes of calculating the maximum dilutive impact, it is presumed that the conversion premium will be settled in common stock, inclusive of a contractual make-whole provision resulting from a fundamental change, and the resulting potential common shares included in diluted earnings per share if the effect is more dilutive.

The stock options, warrants and conversion premium on the Convertible Notes are excluded from the calculation of diluted loss per share because the net loss for the years ended December 31, 2015, 2014 and 2013 causes such securities to be anti-dilutive. Securities excluded from the calculation of diluted loss per share are shown in the chart below:


	Years ended December 31,
(in thousands)	2015		2014		2013
Common stock warrants		—		2,381		2,777
Outstanding options to purchase common stock		19,211		19,567		20,107
Conversion of the Convertible Notes		25,000		25,000		25,000

Product Revenue Reserves and Allowances

12 Months Ended

Dec. 31, 2015

Text Block [Abstract]

Product Revenue Reserves and Allowances

4. Product Revenue Reserves and Allowances

The following table summarizes activity in each of the product revenue reserve and allowance categories for the year ended December 31, 2015:


(in thousands)	Trade Allowances			Rebates and Chargeback Discounts			Product Returns		Other Incentives		Total
Beginning balance	$	—		$	—		$	—	$	—	$	—
Provisions related to sales in the current year		153			456			32		8		649
Adjustments related to sales in the prior year		—			—			—		—		—
Credits and payments made		(15	)		(94	)		—		—		(109	)

Ending balance	$	138		$	362		$	32	$	8	$	540

License and Collaboration Agreements

12 Months Ended

Dec. 31, 2015

Organization, Consolidation and Presentation of Financial Statements [Abstract]

License and Collaboration Agreements

5. License and Collaboration Agreements

Baxalta

On September 23, 2014, the Company and Baxter International Inc., Baxter Healthcare Corporation and Baxter Healthcare SA entered into a license and collaboration agreement (the “Baxalta Agreement”) for the development and commercialization of MM-398 outside of the United States and Taiwan (the “Licensed Territory”). In connection with Baxter International Inc.’s separation of the Baxalta business, the Baxalta Agreement was assigned to Baxalta during the second quarter of 2015. As part of the Baxalta Agreement, the Company granted Baxalta an exclusive, royalty-bearing right and license under the Company’s patent rights and know-how to develop and commercialize MM-398 in the Licensed Territory. Baxalta is responsible for using commercially reasonable efforts to develop, obtain regulatory approvals for and, following regulatory approval, commercializing MM-398 in the Licensed Territory. A joint steering committee comprised of an equal number of representatives from each of Baxalta and the Company is responsible for approving changes to the global development plan for MM-398, including all budgets, and overseeing the parties’ development and commercialization activities with respect to MM-398. Unless otherwise agreed, the Company will be responsible for conducting all clinical trials contemplated by the global development plan for MM-398 and manufacturing all clinical material needed for such trials.

Under the terms of the Baxalta Agreement, the Company received a $100.0 million upfront, nonrefundable cash payment in September 2014. In addition, the Company is eligible to receive from Baxalta (i) up to an aggregate of $100.0 million upon the achievement of specified research and development milestones, of which the Company has received $62.5 million from Baxalta through December 31, 2015, (ii) up to an aggregate of $520.0 million upon the achievement of specified regulatory milestones, of which the Company has received $20.0 million from Baxalta as of December 31, 2015, and (iii) up to an aggregate of $250.0 million upon the achievement of specified sales milestones. Under the terms of the Baxalta Agreement, the Company will bear up to the first $98.8 million of costs related to the development of MM-398 for pancreatic cancer patients who have not previously received gemcitabine-based therapy; however, the Company expects most of these costs to be offset by payments received upon the achievement of clinical trial-related milestones. The Company and Baxalta will share equally all other clinical trial costs contemplated by the global development plan. The Company is also entitled to tiered, escalating royalties ranging from sub-teen double-digits to low twenties percentages of net sales of MM-398 in the Licensed Territory.

The Company and Baxalta expect to enter into a commercial supply agreement pursuant to which the Company will supply MM-398 bulk drug substance to Baxalta and, at Baxalta’s option, may manage fill and finish activities to be conducted by a third-party contract manufacturer for Baxalta. Baxalta also has the option to manufacture MM-398 itself, in which case the Company will perform a technology transfer of its manufacturing process to Baxalta.

If not terminated earlier by either party, the Baxalta Agreement will expire upon expiration of all royalty and other payment obligations of Baxalta under the Baxalta Agreement. Either party may terminate the Baxalta Agreement in the event of an uncured material breach by the other party. Baxalta may also terminate the Baxalta Agreement on a product-by-product, country-by-country or sub-territory-by-sub-territory basis or in its entirety, for its convenience, upon 180 days’ prior written notice. In addition, the Company may terminate the Baxalta Agreement if Baxalta challenges or supports any challenge of the Company’s licensed patent rights.

At the inception of the collaboration, the Company identified the following deliverables as part of the Baxalta Agreement: (i) license to develop and commercialize MM-398 in Baxalta’s territories, (ii) discovery, research, development and manufacturing services required to complete ongoing clinical trials related to MM-398, (iii) discovery, research, development and manufacturing services needed to complete future clinical trials in further indications related to MM-398, (iv) the option to perform a technology transfer of the Company’s manufacturing process related to the production of MM-398 to Baxalta and (v) participation on the joint steering committee.

The Company concluded that none of the deliverables identified at the inception of the collaboration has standalone value from the other undelivered elements. As such, all deliverables represent a single unit of accounting.

The Company has determined that the collaboration represents a services agreement and as such has estimated the level of effort expected to be completed as a result of providing the identified deliverables. The Company will recognize revenue from the non-refundable upfront payment, forecasted non-substantive milestone payments and estimated payments related to discovery, research, development and technology transfer services based on proportional performance as effort is completed over the expected services period, which is estimated to be substantially complete by June 30, 2020. The Company will periodically review and, if necessary, revise the estimated service period related to its collaboration with Baxalta. As of December, 31, 2015, the Company has achieved $62.5 million of the $90.0 million of forecasted non-substantive milestones milestones that are included in the Company’s proportional performance revenue recognition model and $20.0 million of the $530.0 million of substantive milestones included in the Baxalta Agreement.

Research, development and regulatory milestones that are considered substantive on the basis of the contingent nature of the milestone will be recognized as revenue in full in the period in which the associated milestone is achieved, assuming all other revenue recognition criteria are met. All sales milestones will be accounted for in the same manner as royalties and recorded as revenue upon achievement of the milestone, assuming all other revenue recognition criteria are met.

During the second quarter of 2015, the European Medicines Agency (“EMA”) accepted for review a Marketing Authorization Application (“MAA”) filed by Baxalta for MM-398. As a result of this acceptance, the Company recognized $20.0 million of revenue related to a substantive milestone payment owed from Baxalta. In August 2015, the Company achieved a $15.0 million milestone related to the submission of the protocol for the Company’s Phase 2 clinical trial of MM-398 in front-line metastatic pancreatic cancer. This milestone is a non-substantive milestone, and revenue related to the achievement of this milestone will be recognized through the proportional performance revenue recognition model. In October 2015, the Company achieved an additional $47.5 million milestone related to the enrollment of the first patient in a Phase 2 clinical trial of MM-398 in front-line pancreatic cancer. This milestone is also a non-substantive milestone, and revenue related to the achievement of this milestone will be recognized through the proportional performance revenue recognition model. During the years ended December 31, 2015 and 2014, the Company recognized revenue based on the following components of the Baxalta Agreement:


	Year Ended December 31,		Year Ended December 31,
(in thousands)	2015		2014
Proportional performance revenue recognition model	$	64,930	$	10,460
Substantive milestones		20,000		—

Total	$	84,930	$	10,460

As of December 31, 2015 and 2014, the Company maintained the following assets and liabilities related to the Baxalta Agreement:


(in thousands)	December 31, 2015		December 31, 2014
Accounts receivable, billed	$	1,336	$	—
Accounts receivable, unbilled		626		1,615
Deferred revenue		97,365		91,156

Of the $97.4 million of deferred revenue related to the Baxalta Agreement as of December 31, 2015, $50.1 million is classified as current in the consolidated balance sheets based upon the Company’s estimate of revenue that will be recognized under the proportional performance revenue recognition model as a result of effort expected to be completed within the next twelve months.

Sanofi

On September 30, 2009, the Company and Sanofi entered into a license and collaboration agreement (the “Sanofi Agreement”) for the development and commercialization of MM-121. The Sanofi Agreement became effective on November 10, 2009, and Sanofi paid the Company a nonrefundable, noncreditable upfront license fee of $60.0 million. On June 17, 2014, the Company and Sanofi agreed to terminate the Sanofi Agreement effective December 17, 2014. In connection with the agreement to terminate the Sanofi Agreement, among other things, Sanofi transferred ownership of the investigational new drug application for MM-121 back to the Company in July 2014, and the Company waived Sanofi’s obligation to reimburse the Company for MM-121 development costs incurred after the effective termination date. Following the termination of the Sanofi Agreement, the Company is not entitled to receive any additional fees, milestone payments or reimbursements from the collaboration.

The Company received total milestone payments of $25.0 million pursuant to the Sanofi Agreement. Under the Sanofi Agreement, Sanofi was responsible for all MM-121 development and manufacturing costs. Sanofi reimbursed the Company for direct costs incurred in both development and manufacturing and compensated the Company for its internal development efforts based on a full time equivalent rate.

The Company recognized cost reimbursements for MM-121 development services within the period they were incurred and billable. Billable expenses were identified during each specified budget period. In the event that total development services expense incurred and expected to be incurred during the same period exceeded the total contractually allowed billable amount for development services during that period, the Company recognized only a percentage of the development services incurred as revenue during that period.

At the inception of the collaboration, the Company determined that the license, the right to future technology, back-up compounds, participation on steering committees and manufacturing services performance obligations comprising the Sanofi Agreement represented a single unit of accounting. As the Company could not reasonably estimate its level of effort over the collaboration, the Company recognized revenue from the upfront payment, milestone payment and manufacturing services payments using the contingency-adjusted performance model over the expected development period, which was initially estimated at 12 years from the effective date of the Sanofi Agreement.

As a result of the Company and Sanofi agreeing to terminate the Sanofi Agreement, the development period was revised to end as of December 17, 2014. Accordingly, the balance of the deferred revenue remaining on April 1, 2014 was recognized prospectively on a straight-line basis over the remaining development period, ending on December 17, 2014, in accordance with current generally accepted principles on revenue recognition.

The Company recognized no revenue under the Sanofi agreement during the year ended December 31, 2015. During the years ended December 31, 2014 and 2013, the Company recognized revenue based on the following components of the Sanofi agreement:


	Years ended December 31,
(in thousands)	2014		2013
Upfront payment	$	39,306	$	5,000
Milestone payment		16,377		2,083
Development services		18,904		36,283
Manufacturing services and other		17,709		3,867

Total	$	92,296	$	47,233

The Company performed development services for which revenue was recognized under the Sanofi Agreement in accordance with the specified budget period. During the year and specified budget periods ended December 31, 2013, the Company performed $10.1 million of development services in excess of recognized revenue. Of this amount, approximately $5.8 million was recognized as increased revenue in the year ended December 31, 2014 related to expenses incurred prior to December 31, 2013 upon the Company receiving budget approval for these overruns.

As of December 31, 2015, the Company maintained no assets or liabilities related to the Sanofi Agreement. As of December 31, 2014, the Company maintained the following assets and liabilities related to the Sanofi agreement:


(in thousands)	December 31, 2014
Accounts receivable, billed	$	369
Accounts receivable, unbilled		1,282
Deferred revenues		—

PharmaEngine, Inc.

On May 5, 2011, the Company and PharmaEngine, Inc. (“PharmaEngine”) entered into an assignment, sublicense and collaboration agreement (the “PharmaEngine Agreement”) under which the Company reacquired rights in Europe and certain countries in Asia to MM-398. In exchange, the Company agreed to pay PharmaEngine a nonrefundable, noncreditable upfront payment of $10.0 million and up to an additional $80.0 million in aggregate development and regulatory milestones and $130.0 million in aggregate sales milestones. PharmaEngine is also entitled to tiered royalties on net sales of MM-398 in Europe and certain countries in Asia. PharmaEngine is not responsible for any future development costs of MM-398 except those required specifically for regulatory approval in Taiwan.

On September 22, 2014, the Company amended the PharmaEngine Agreement to redefine sublicense revenue and reduce the portion of sublicense revenue that the Company is required to pay to PharmaEngine. As a result of this amendment, the Company made a $7.0 million milestone payment to PharmaEngine in September 2014. Additionally, as a result of this amendment, the Company agreed to pay a previously contingent $5.0 million milestone to PharmaEngine in the second quarter of 2015. Prior to the amendment of the PharmaEngine Agreement, this milestone payment was contingent upon the award of certain specified regulatory designations. These milestone payments were recognized as research and development expense during the year ended December 31, 2014. The Company also made an $11.0 million milestone payment to PharmaEngine in July 2015 in connection with the EMA’s acceptance for review of an MAA for MM-398, which occurred, and was recognized as research and development expense, in the second quarter of 2015.

During the years ended December 31, 2015, 2014 and 2013, the Company recognized research and development expenses of $11.4 million, $12.6 million and $1.5 million, respectively, related to the PharmaEngine Agreement.

Actavis

In November 2013, the Company and Actavis entered into a development, license and supply agreement (the “Actavis Agreement”) pursuant to which the Company will develop, manufacture and exclusively supply the bulk form of doxorubicin HCl liposome injection (the “Initial Product”) to Actavis. The Actavis Agreement was subsequently amended in January 2015 to transfer certain responsibilities from the Company to Actavis in exchange for reducing the aggregate milestone payments that the Company is eligible to receive by $0.4 million. Under the Actavis Agreement, Actavis is responsible for all costs related to finished product processing and global commercialization. Pursuant to the agreement, additional products may be developed for Actavis in the future. The Company is eligible to receive up to $15.1 million, of which $3.9 million has been received through December 31, 2015, and the remainder in development funding and development, regulatory and commercial milestone payments related to the Initial Product. The Company will also receive a double-digit share of net profits on global sales of the Initial Product and any additional products. The Company will manufacture and supply the Initial Product to Actavis in bulk form at an agreed upon unit price.

The Actavis Agreement will expire with respect to the Initial Product and any additional products developed in the future ten years after Actavis’ first sale of the applicable product, unless terminated earlier, and will automatically renew for additional two year periods thereafter unless either party provides notice of non-renewal. Either party may terminate the Actavis Agreement in the event of an uncured material breach or bankruptcy filing by the other party. Actavis may also terminate the Actavis Agreement for convenience in specified circumstances upon 90 days’ prior written notice.

The Company applied revenue recognition guidance to determine whether the performance obligations under this collaboration, including the license, participation on steering committees, development services, and manufacturing and supply services could be accounted for separately or as a single unit of accounting. The Company determined that these obligations represent a single unit of accounting and will recognize revenue as product is supplied to Actavis. Therefore, the Company has recorded $4.0 million and $3.8 million of billed and billable milestones and development expenses related to the Actavis Agreement as deferred revenue as of December 31, 2015 and 2014, respectively. This revenue is expected to be recognized by the Company over the ten year period that begins after Actavis’ first sale of the applicable product under the Actavis Agreement.

Fair Value of Financial Instruments

12 Months Ended

Dec. 31, 2015

Fair Value Disclosures [Abstract]

Fair Value of Financial Instruments

6. Fair Value of Financial Instruments

The carrying values of cash, restricted cash, prepaid expenses, accounts receivable, accounts payable and accrued expenses, and other short-term assets and liabilities approximate their respective fair values due to the short-term maturities of these assets and liabilities.

Fair value is an exit price, representing the amount that would be received from the sale of an asset or paid to transfer a liability in an orderly transaction between market participants. Fair value is determined based on observable and unobservable inputs. Observable inputs reflect readily obtainable data from independent sources, while unobservable inputs reflect certain market assumptions. As a basis for considering such assumptions, GAAP establishes a three-tier value hierarchy, which prioritizes the inputs used to develop the assumptions and for measuring fair value as follows: (Level 1) observable inputs such as quoted prices in active markets for identical assets; (Level 2) inputs other than the quoted prices in active markets that are observable either directly or indirectly; and (Level 3) unobservable inputs in which there is little or no market data, which requires the Company to develop its own assumptions. This hierarchy requires the Company to use observable market data, when available, and to minimize the use of unobservable inputs when determining fair value.

Recurring Fair Value Measurements

The following tables show assets measured at fair value on a recurring basis as of December 31, 2015 and 2014 and the input categories associated with those assets:


As of December 31, 2015 (in thousands)	Level 1		Level 2		Level 3
Assets:
Cash equivalents – money market funds	$	704	$	—	$	—
Marketable securities – commercial paper		—		—		—
Marketable securities – corporate debt securities		—		—		—

As of December 31, 2014 (in thousands)	Level 1		Level 2		Level 3
Assets:
Cash equivalents – money market funds	$	33,199	$	—	$	—
Marketable securities – commercial paper		—		6,491		—
Marketable securities – corporate debt securities		—		81,849		—

There have been no impairments of the above assets measured and carried at fair value during the years ended December 31, 2015 or 2014. In addition, there were no changes in valuation techniques or transfers between the fair value measurement levels during the years ended December 31, 2015 or 2014.

There were no liabilities measured at fair value on a recurring basis as of December 31, 2015 and 2014.

Non-Recurring Fair Value Measurements

Certain assets, including IPR&D, may be measured at fair value on a non-recurring basis in periods subsequent to initial recognition. No non-recurring fair value measurements were required during the years ended December 31, 2015 or 2014.

Other Fair Value Measurements

The estimated fair value of the $125.0 million aggregate principal amount of the Convertible Notes was $184.6 million as of December 31, 2015. The Company estimated the fair value of the Convertible Notes by using a quoted market rate in an inactive market, which is classified as a Level 2 input. The carrying value of the Convertible Notes is $88.5 million as of December 31, 2015 due to the bifurcation of the conversion feature of the Convertible Notes as described more fully in Note 11, “Borrowings.”

As discussed in Note 11, “Borrowings,” in December 2015, the Company closed a private placement of $175.0 million aggregate principal amount of 11.50% senior secured notes due 2022 (the “2022 Notes”). The carrying value of the 2022 Notes was $169.2 million as of December 31, 2015. The fair value of the 2022 Notes approximated their face value of $175.0 million as of December 31, 2015.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Consolidated Subsidiaries	12 Months Ended
Consolidated Subsidiaries	Dec. 31, 2015
Text Block [Abstract]
Consolidated Subsidiaries	7. Consolidated Subsidiaries Silver Creek Pharmaceuticals, Inc. On August 20, 2010, the Company acquired a controlling interest in Silver Creek. The Company has concluded that Silver Creek is a variable interest entity and the Company is the primary beneficiary. The Company has the ability to direct the activities of Silver Creek through its ownership percentage and through the board of director seats controlled by the Company and its de facto agents. As such, Silver Creek is consolidated by the Company. In December 2012, as described in Note 11, “Borrowings,” Silver Creek entered into a Note Purchase Agreement pursuant to which it issued convertible notes to various lenders in aggregate principal amounts of $1.6 million in December 2012, $0.3 million in February 2013 and $0.6 million in December 2013. As of December 31, 2013, these outstanding borrowings and related accrued interest of $2.6 million converted to shares of Silver Creek Series A preferred stock at the Series A preferred stock value of $1.00 per share. As a result of changes to the ownership composition of Silver Creek as of December 31, 2013, the non-controlling interest in Silver Creek increased by $0.8 million. During the year ended December 31, 2014, Silver Creek issued convertible notes to various lenders in the aggregate principal amount of $1.0 million. As of December 31, 2014, these outstanding borrowings and an immaterial amount of related accrued interest converted to shares of Silver Creek Series A preferred stock at the Series A preferred stock value of $1.00 per share. As a result of changes to the ownership composition of Silver Creek as of December 31, 2014, the non-controlling interest in Silver Creek increased by approximately $0.4 million. During the year ended December 31, 2015, Silver Creek issued and sold a total of 1.6 million shares of Silver Creek Series B preferred stock at a price per share of $1.35 to investors and received net proceeds of $2.1 million, after deducting issuance costs. As a result of changes to the ownership composition of Silver Creek as of December 31, 2015, the non-controlling interest in Silver Creek increased by approximately $0.9 million. As of December 31, 2015 and 2014, the Company owned approximately 56% and 60% of the voting stock of Silver Creek, respectively, and recorded a non-controlling interest of approximately $0.2 million and $0.1 million, respectively, as a component of mezzanine equity on the Company’s consolidated balance sheets based on the terms of the Silver Creek Series A and Series B preferred stock. As of December 31, 2015, the Company consolidated Silver Creek’s total assets and total liabilities of $0.8 million and $0.2 million, respectively. As of December 31, 2014, the Company consolidated Silver Creek’s total assets and total liabilities of $0.3 million and $0.2 million, respectively. As of December 31, 2015 and 2014, the Company’s unrestricted cash and cash equivalents balance includes $0.7 million and $0.3 million, respectively, of cash and cash equivalents held by Silver Creek. The cash and cash equivalents held by Silver Creek as of December 31, 2015 are designated for the operations of Silver Creek. Merrimack Pharmaceuticals (Bermuda) Ltd. Merrimack Pharmaceuticals (Bermuda) Ltd. was incorporated in Bermuda during 2011 and merged with and into the Company during the third quarter of 2014.

Goodwill and Intangible Assets, Net

12 Months Ended

Dec. 31, 2015

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill and Intangible Assets, Net

8. Goodwill and Intangible Assets, Net

As part of the acquisition of Hermes on October 6, 2009 (the “Acquisition Date”), the Company recognized acquired IPR&D of $7.0 million related to several development programs: an antibody-targeted nanotherapeutic that contains a chemotherapy drug, a nanotherapeutic that contains a chemotherapy drug and other early-stage preclinical programs in the amounts of $2.8 million, $3.4 million and $0.8 million, respectively. The Company also acquired intangible assets of $3.2 million related to core nano-carrier technology. These values were determined at the time of acquisition by estimating the costs to develop the acquired IPR&D into commercially viable products, estimating the net cash flows from such projects and discounting the net cash flows back to their present values. The probability of success factors and discount rates used for each project considered the uncertainty surrounding the successful development of the acquired IPR&D.

During the fourth quarter of 2015, upon the approval of ONIVYDE by the FDA, the Company reclassified the acquired IPR&D asset related to the nanotherapeutic that contains a chemotherapy drug to definite-lived intangible assets and commenced amortization. This definite-lived ONIVYDE intangible asset is amortized on a straight-line basis through 2028. Amortization of the acquired IPR&D asset related to the antibody-targeted nanotherapeutic that contains a chemotherapy drug has not commenced as of December 31, 2015. The deprioritization and delay of the other early-stage preclinical programs during the year ended December 31, 2013 resulted in an impairment charge of $0.8 million recognized during the third quarter of 2013. The core nano-carrier technology intangible asset is being amortized on a straight-line basis over a period of ten years, which is management’s best estimate of the useful life of this technology. The weighted-average remaining amortization period for the Company’s intangible assets subject to amortization is approximately 10.6 years as of December 31, 2015.

Changes in the carrying value of the nano-carrier technology intangible asset, the ONIVYDE intangible asset, IPR&D and goodwill for the years ended December 31, 2015 and 2014 were as follows:


(in thousands)	Nano-carrier technology intangible asset			ONIVYDE intangible asset			IPR&D			Goodwill
Balance, December 31, 2013	$	1,845		$	—		$	6,200		$	3,605
Amortization		(320	)		—			—			—

Balance, December 31, 2014		1,525			—			6,200			3,605
Reclassification of IPR&D to definite-lived intangible assets		—			3,400			(3,400	)		—
Amortization		(320	)		(50	)		—			—

Balance, December 31, 2015	$	1,205		$	3,350		$	2,800		$	3,605

Amortization expense is expected to be as follows for the next five-year period:


Years Ended December 31,	(in thousands)
2016	$	578
2017		578
2018		578
2019		503
2020		258

- Definition

The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final. May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.

+ References + Details

Property and Equipment, Net

12 Months Ended

Dec. 31, 2015

Property, Plant and Equipment [Abstract]

Property and Equipment, Net

9. Property and Equipment, Net

Property and equipment, net as of December 31, 2015 and 2014 consisted of the following:


	December 31,
(in thousands)	2015			2014
Lab equipment	$	19,305		$	16,214
IT equipment		7,742			3,113
Leasehold improvements		21,026			18,219
Furniture and fixtures		910			624
Construction in process		2,243			472

Total property and equipment, gross		51,226			38,642
Less: Accumulated depreciation		(29,311	)		(24,140	)

Total property and equipment, net	$	21,915		$	14,502

Depreciation expense was $5.5 million, $4.2 million and $2.8 million for the years ended December 31, 2015, 2014 and 2013, respectively. Capitalized interest costs were insignificant for the years ended December 31, 2015, 2014 and 2013.

During the years ended December 31, 2015, 2014 and 2013, the Company disposed of $0.3 million, $1.6 million and $0.2 million, respectively, of fully depreciated assets. There were no recognized impairment charges related to fixed assets in the years ended December 31, 2015, 2014 or 2013.

Accounts Payables, Accrued Expenses and Other

12 Months Ended

Dec. 31, 2015

Payables and Accruals [Abstract]

Accounts Payables, Accrued Expenses and Other

10. Accounts Payables, Accrued Expenses and Other

Accounts payable, accrued expenses and other as of December 31, 2015 and 2014 consisted of the following:


	December 31,
(in thousands)	2015		2014
Accounts payable	$	5,049	$	2,510
Accrued goods and services		14,295		17,481
Accrued clinical trial costs		12,764		7,637
Accrued drug purchase costs		7,460		—
Accrued payroll and related benefits		9,009		6,166
Accrued interest		3,041		2,956
Accrued dividends payable		19		19
Deferred tax incentives		445		467

Total accounts payable, accrued expenses and other	$	52,082	$	37,236

Borrowings

12 Months Ended

Dec. 31, 2015

Debt Disclosure [Abstract]

Borrowings

11. Borrowings

2022 Notes

On December 22, 2015, the Company closed a private placement of $175.0 million aggregate principal amount of 11.50% 2022 Notes and entered into an indenture (the “U.S. Bank indenture”) with U.S. Bank National Association as trustee and collateral agent (the “2020 Notes Trustee”). As a result of this placement, the Company received net proceeds of approximately $168.5 million, after deducting private placement and offering expenses payable by the Company. The private placement and offering expenses included $0.9 million of transaction costs that were expensed in accordance with the debt modification guidance per Accounting Standards Codification (“ASC”) 480, as further discussed below. The 2022 Notes bear interest at a rate of 11.50% per year, payable semi-annually on June 15 and December 15 of each year, beginning on June 15, 2016. The Company will pay semi-annual installments of principal on the 2022 Notes of $21,875,000 each, subject to adjustment as provided in the 2022 Notes, on June 15 and December 15 of each year, beginning on June 15, 2019. The 2022 Notes will mature on December 15, 2022, unless earlier redeemed or repurchased in accordance with their terms prior to such date.

The Company may redeem the 2022 Notes at its option, in whole or in part from time to time at a price equal to the principal amount plus accrued interest and a specified make-whole premium. If the Company experiences certain change of control events as defined in the U.S. Bank Indenture, the holders of the 2022 Notes will have the right to require the Company to purchase all or a portion of the 2022 Notes at a purchase price in cash equal to 101% of the principal amount thereof, plus accrued and unpaid interest to the date of purchase. In addition, upon certain asset sale events as defined in the U.S. Bank Indenture, the Company may be required to offer to use the net proceeds thereof to purchase all or a portion of the 2022 Notes at 100% of the principal amount thereof, plus accrued and unpaid interest to the date of purchase.

The 2022 Notes are senior secured obligations of the Company and will be equal in right of payment to all existing and future pari passu indebtedness of the Company (including the Company’s outstanding Convertible Notes), will be senior in right of payment to all existing and future subordinated indebtedness of the Company, will have the benefit of a security interest in the 2022 Notes collateral and will be junior in lien priority in respect of any asset-based lending collateral that secures any first priority lien obligations from time to time. The 2022 Notes contain customary covenants, including covenants that limit or restrict the Company’s ability to incur liens, incur indebtedness, and make certain restricted payments, but do not contain covenants related to future financial performance. The 2022 Notes are secured by a first priority lien on substantially all of the Company’s assets.

The 2022 Notes contain customary events of default. Upon certain events of default occurring, the 2022 Notes Trustee may declare 100% of the principal of and accrued and unpaid interest, if any, on all the 2022 Notes to be due and payable. In the case of certain events of bankruptcy, insolvency or reorganization involving the Company or a restricted subsidiary, 100% of the principal of, and accrued and unpaid interest on, the 2022 Notes will automatically become due and payable. There have been no events of default as of or during the year ended December 31, 2015.

The Company assessed the 2022 Notes pursuant to ASC 815 to determine if any features necessitated bifurcation from the host instrument. The Company concluded that none of the embedded redemption features within the 2022 Notes require bifurcation as these features are clearly and closely related to the host instrument.

A portion of the proceeds from the issuance of the 2022 Notes were used to repay the Company’s outstanding $40.0 million of loans payable under the Loan Agreement with Hercules, as further discussed below. The remaining proceeds will be used to fund future operations of the Company.

Debt issuance costs incurred by the Company, excluding costs allocated to the debt modification as discussed below, are accounted for as a direct deduction to the carrying value of the 2022 Notes and are amortized to interest expense using the effective interest method over the life of the 2022 Notes. The effective interest rate associated with the 2022 Notes is 12.32%. For the year ended December 31, 2015, interest expense related to the 2022 Notes was approximately $0.5 million.

Convertible Notes

In July 2013, the Company issued $125.0 million aggregate principal amount of Convertible Notes in an underwritten public offering. The Company issued the Convertible Notes under an indenture, dated as of July 17, 2013 (the “Base Indenture”) between the Company and Wells Fargo Bank, National Association, as trustee (the “Convertible Notes Trustee”), as supplemented by the supplemental indenture, dated as of July 17, 2013, between the Company and the Convertible Notes Trustee (together with the Base Indenture, the “Wells Fargo Indenture”). As a result of the Convertible Notes offering, the Company received net proceeds of approximately $120.6 million, after deducting underwriting discounts and commissions and offering expenses payable by the Company.

The Convertible Notes bear interest at a rate of 4.50% per year, payable semiannually in arrears on January 15 and July 15 of each year, beginning on January 15, 2014. The Convertible Notes are general unsecured senior obligations of the Company and rank (i) pari passu in seniority with respect to the 2022 Notes, (ii) senior in right of payment to any of the Company’s indebtedness that is expressly subordinated in right of payment to the Convertible Notes, (iii) equal in right of payment to any of the Company’s unsecured indebtedness that is not so subordinated, (iv) effectively junior in right of payment to any of the Company’s secured indebtedness to the extent of the value of the assets securing such indebtedness and (v) structurally junior to all indebtedness and other liabilities (including trade payables) of the Company’s subsidiaries.

The Convertible Notes will mature on July 15, 2020 (the “Maturity Date”), unless earlier repurchased by the Company or converted at the option of holders. Holders may convert their Convertible Notes at their option at any time prior to the close of business on the business day immediately preceding April 15, 2020 only under the following circumstances:

•

during any calendar quarter commencing after September 30, 2013 (and only during such calendar quarter), if the last reported sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day;

•

during the five business day period after any five consecutive trading day period (the “measurement period”) in which the trading price (as defined in the Convertible Notes) per $1,000 principal amount of Convertible Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate on each such trading day; or

•

upon the occurrence of specified corporate events set forth in the Wells Fargo Indenture.

During the fourth quarter of 2015, the last reported sale price of the common stock for at least 20 trading days (whether or not consecutive) during the period of 30 consecutive trading days ending on the last trading day of the calendar quarter ended December 31, 2015 was greater than 130% of the conversion price for the Convertible Notes on each applicable trading day. As a result, holders may convert their Convertible Notes at their option at any time from January 1, 2016 through March 31, 2016.

On or after April 15, 2020 until the close of business on the business day immediately preceding the Maturity Date, holders may convert their Convertible Notes at any time, regardless of the foregoing circumstances.

Following the repayment and satisfaction in full of the Company’s obligations to Hercules under the Loan Agreement, which occurred in December 2015, upon any conversion of the Convertible Notes, the Convertible Notes may be settled, at the Company’s election, in cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock.

The initial conversion rate of the Convertible Notes is 160 shares of the Company’s common stock per $1,000 principal amount of Convertible Notes, which is equivalent to an initial conversion price of $6.25 per share of common stock. The conversion rate will be subject to adjustment in some events, but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the Maturity Date, the Company will increase the conversion rate for a holder who elects to convert its Convertible Notes in connection with such a corporate event in certain circumstances.

Upon the occurrence of a fundamental change (as defined in the Wells Fargo Indenture) involving the Company, holders of the Convertible Notes may require the Company to repurchase all or a portion of their Convertible Notes for cash at a price equal to 100% of the principal amount of the Convertible Notes to be purchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.

The Wells Fargo Indenture contains customary terms and covenants and events of default with respect to the Convertible Notes. If an event of default (as defined in the Wells Fargo Indenture) occurs and is continuing, the Convertible Notes Trustee by written notice to the Company, or the holders of at least 25% in aggregate principal amount of the Convertible Notes then outstanding by written notice to the Company and the Convertible Notes Trustee, may, and the Convertible Notes Trustee at the request of such holders will, declare 100% of the principal of and accrued and unpaid interest on the Convertible Notes to be due and payable. In the case of an event of default arising out of certain events of bankruptcy, insolvency or reorganization involving the Company or a significant subsidiary (as set forth in the Indenture), 100% of the principal of and accrued and unpaid interest on the Convertible Notes will automatically become due and payable. There have been no events of default as of or during the year ended December 31, 2015.

The Company has separately accounted for the liability and equity components of the Convertible Notes by bifurcating gross proceeds between the indebtedness, or liability component, and the embedded conversion option, or equity component. This bifurcation was done by estimating an effective interest rate as of the date of issuance for similar notes which do not contain an embedded conversion option. This effective interest rate was estimated to be 15% and was used to compute the initial fair value of the indebtedness of $71.2 million. The gross proceeds received from the issuance of the Convertible Notes less the initial amount allocated to the indebtedness resulted in a $53.8 million allocation to the embedded conversion option. The embedded conversion option was recorded in stockholders’ deficit and as debt discount, to be subsequently amortized as interest expense over the term of the Convertible Notes. Underwriting discounts and commissions and offering expenses totaled $4.4 million and were allocated to the indebtedness and the embedded conversion option based on their relative values. As a result, $2.5 million attributable to the indebtedness was recorded as debt discount, to be subsequently amortized as interest expense over the term of the Convertible Notes, and $1.9 million attributable to the embedded conversion option was netted with the embedded conversion option in stockholders’ deficit.

For the years ended December 31, 2015, 2014 and 2013, interest expense related to the outstanding principal balance of the Convertible Notes was $13.7 million, $13.7 million and $6.2 million, respectively.

Loan Agreement

In November 2012, the Company entered into the Loan Agreement with Hercules pursuant to which the Company received loans in the aggregate principal amount of $40.0 million. The Company, as permitted under the Loan Agreement, had previously extended the interest-only payment period with the aggregate principal balance of the loans to be repaid in monthly installments starting on June 1, 2014 and continuing through November 1, 2016. On June 25, 2014, the Company entered into an amendment to the Loan Agreement, whereby the Company and Hercules agreed to extend until October 1, 2014 the period during which the Company makes interest-only payments. On November 6, 2014, the Company entered into a further amendment to the Loan Agreement, whereby the Company and Hercules agreed to extend by four additional months the period during which the Company makes interest-only payments. On February 25, 2015, the Company entered into a fourth amendment to the Loan Agreement pursuant to which the Company and Hercules agreed to extend the maturity date and the period during which the Company makes interest-only payments on its current loans in the aggregate principal amount of $40.0 million. As a result of this amendment, the Company was required to repay the outstanding aggregate principal balance of the loan beginning on June 1, 2016 and continuing through November 1, 2018. As a result of the FDA’s approval of the Company’s NDA for ONIVYDE, which occurred on October 22, 2015, the Company elected to extend the interest-only period by an additional six months such that the Company would repay the outstanding aggregate principal balance of the loans beginning on December 1, 2016 and continuing through November 1, 2018. This amendment was treated as a debt modification for accounting purposes.

Upon the earlier of full repayment of the loans or November 1, 2016, the Company was required to pay Hercules a fee of $1.2 million, which had been recorded as a discount to the loans and as a long-term liability on the Company’s consolidated balance sheets. Additionally, the Company reimbursed Hercules for costs incurred related to the loans, which was reflected as a discount to the carrying value of the loans. The Company amortized these loan discounts totaling $1.6 million to interest expense over the term of the loans using the effective interest method.

In connection with the Loan Agreement, the Company granted Hercules a security interest in all of the Company’s personal property now owned or hereafter acquired, excluding intellectual property but including the proceeds from the sale, if any, of intellectual property, and a negative pledge on intellectual property. The Loan Agreement also contained certain representations, warranties and non-financial covenants of the Company.

During the fourth quarter of 2015, the Company repaid the loans in full in conjunction with the issuance of the 2022 Notes. The total repayment amount included the $40.0 million in outstanding principal, the $1.2 million fee discussed above and interest accrued up through the repayment date. The Company assessed the repayment of the Loan Agreement with Hercules in conjunction with the issuance of the 2022 Notes, of which Hercules holds a portion, in accordance with the debt extinguishment and modification guidance per ASC 480. Based upon this assessment, the Company concluded that this transaction represented a debt modification, and accordingly, $0.3 million of unamortized debt issuance costs related to the Loan Agreement will be amortized as an adjustment of interest expense over the life of the 2022 Notes using the effective interest method. In addition, $0.9 million of debt issuance costs associated with the 2022 Notes were allocated to the modified Loan Agreement and expensed as a component of “Interest expense” on the consolidated statement of operations and comprehensive loss for the year ended December 31, 2015.

For the years ended December 31, 2015, 2014 and 2013, interest expense related to the Hercules loans was $5.4 million, $4.7 million and $4.9 million, respectively.

Convertible Notes—Silver Creek

In December 2012, the Company’s majority owned subsidiary, Silver Creek, entered into a Note Purchase Agreement pursuant to which it issued convertible notes to various lenders in aggregate principal amounts of $1.6 million in December 2012, $0.9 million during the year ended December 31, 2013 and $1.0 million during the year ended December 31, 2014. The notes issued pursuant to the Note Purchase Agreement bore interest at 6% per annum. Upon issuance, these convertible notes contained a feature wherein if at any time prior to maturity Silver Creek enters into a qualifying equity financing, defined as a sale or series of related sales of equity securities prior to the maturity date and resulting in at least $4.0 million of gross proceeds, the notes would automatically convert into the next qualifying equity financing at a 25% discount. The Company determined that this convertible feature met the definition of a derivative and required separate accounting treatment. The derivative was estimated to be valued at $0.2 million for the year ended December 31, 2012 using a probability-weighted model and was recorded as derivative liability on the consolidated balance sheets. For the years ended December 31, 2014 and 2013, the derivative was remeasured upon conversion of the notes with the gain in remeasurement recognized in other income. The specific notes that were outstanding as of December 31, 2014 and 2013 matured and converted, along with an immaterial amount of accrued interest into shares of Silver Creek Series A preferred stock on both December 31, 2014 and 2013. Upon conversion, the Company’s ownership percentage of Silver Creek outstanding preferred stock decreased from 74% as of December 31, 2012 to 64% as of December 31, 2013 to 60% as of December 31, 2014, and a $0.4 million and $0.8 million increase to non-controlling interest was recognized as of December 31, 2014 and December 31, 2013, respectively.

Future Minimum Payments under Outstanding Borrowings

Future minimum payments under outstanding borrowings as of December 31, 2015 are as follows:


(in thousands)	Convertible Notes			2022 Notes
2016	$	5,625		$	19,734
2017		5,625			20,125
2018		5,625			20,125
2019		5,625			62,617
2020 and thereafter		130,625			157,664

Total	$	153,125		$	280,265
Less interest		(28,125	)		(105,265	)
Less unamortized discount		(36,505	)		(5,840	)
Less current portion		—			—

Long-term debt, net of current portion	$	88,495		$	169,160

Inventory

12 Months Ended

Dec. 31, 2015

Inventory Disclosure [Abstract]

Inventory

12. Inventory

Inventory consists of the following as of December 31, 2015:


(in thousands)	December 31, 2015
Raw materials	$	900
Work in process		2,743
Finished goods		74

Total inventory	$	3,717

Inventory acquired prior to receipt of marketing approval of ONIVYDE was expensed as research and development expense as incurred. The Company began to capitalize the costs associated with the production of ONIVYDE upon receipt of FDA approval on October 22, 2015.

Stock Warrants

12 Months Ended

Dec. 31, 2015

Text Block [Abstract]

Stock Warrants

13. Stock Warrants

The following is a description of the common stock warrant activity of the Company:


(in thousands, except per share amounts)	Warrants for the Purchase of Common Stock			Weighted Average Exercise Price
Balance—December 31, 2012		2,842		$	3.05
Exercised		(65	)	$	2.82

Balance—December 31, 2013		2,777		$	3.05
Exercised		(396	)	$	3.38

Balance—December 31, 2014		2,381		$	3.00
Exercised		(2,355	)	$	3.00
Cancelled		(26	)	$	3.00

Balance—December 31, 2015		—		$	—

During the year ended December 31, 2013, warrants to purchase approximately 65,000 shares of common stock were cashless exercised and 35,000 shares of common stock were issued. During the year ended December 31, 2014, warrants to purchase approximately 75,000 shares of common stock were cashless exercised and 38,000 shares of common stock were issued. During the year ended December 31, 2015, warrants to purchase approximately 2,295,000 shares of common stock were cashless exercised and 1,695,000 shares of common stock were issued. As of December 31, 2015, all remaining unexercised warrants for the purchase of common stock had expired and were cancelled.

Common Stock

12 Months Ended

Dec. 31, 2015

Equity [Abstract]

Common Stock

14. Common Stock

In July 2013, the Company sold an aggregate of 5.8 million shares of its common stock at a price to the public of $5.00 per share in an underwritten public offering and received net proceeds of approximately $26.7 million, after deducting underwriting discounts and commissions and offering expenses payable by the Company.

In July 2015, the Company entered into a Sales Agreement with Cowen and Company, LLC (“Cowen”) to sell shares of the Company’s common stock having an aggregate sales price of up to $40.0 million through an “at the market offering” program under which Cowen acted as the sales agent. The Company concluded sales under this program in September 2015, having sold approximately 3.8 million shares of common stock and generating approximately $38.6 million in net proceeds, after deducting commissions and offering expenses.

As of December 31, 2015 and 2014, the Company had 200.0 million shares of $0.01 par value common stock authorized. There were approximately 115.9 million and 106.7 million shares of common stock issued and outstanding as of December 31, 2015 and 2014, respectively. The shares reserved for future issuance as of December 31, 2015 and 2014 consisted of the following:


(in thousands)	December 31, 2015		December 31, 2014
Common stock warrants		—		2,381
Outstanding options to purchase common stock		19,211		19,567
Shares available for future issuance under 2011 Stock Incentive Plan		2,462		1,983
Conversion of the Convertible Notes		25,000		25,000

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(d),(e))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21484-112644

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SAB TOPIC 4.E)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74512-122707

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21488-112644

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29-31)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB TOPIC 4.C)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187143-122770

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
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-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21506-112644

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
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-Paragraph 2
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Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21475-112644

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Preferred Stock
-URI http://asc.fasb.org/extlink&oid=6521494

Reference 12: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

Reference 13: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21564-112644

Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 4
-Section E

Reference 15: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 4
-Section C

+ Details

Stock-Based Compensation

12 Months Ended

Dec. 31, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-Based Compensation

15. Stock-Based Compensation

In 2008, the Company adopted the 2008 Stock Incentive Plan (as amended, the “2008 Plan”) for employees, officers, directors, consultants and advisors. The 2011 Stock Incentive Plan (the “2011 Plan”) became effective upon closing of the Company’s initial public offering in April 2012. Upon effectiveness of the 2011 Plan, no further awards were available to be issued under the 2008 Plan. The 2011 Plan is administered by the Board of Directors of the Company and permits the Company to grant incentive and non-qualified stock options, stock appreciation rights, restricted stock, restricted stock units and other stock-based awards. Additional shares also become available for grant by reason of the forfeiture, cancellation, expiration or termination of existing awards. The Company registered 3.4 million, 3.6 million and 3.7 million of additional shares of common stock related to the 2011 Plan in February 2013, March 2014 and February 2015, respectively. As of December 31, 2015, there were 2.5 million shares remaining available for grant under the 2011 Plan.

During the years ended December 31, 2015, 2014 and 2013, the Company issued options to purchase 3.7 million, 3.9 million and 3.3 million shares of common stock, respectively. These options generally vest over a three-year period for employees. Options granted to directors during the period from April 2012 through December 2013 vest over a one-year period. All other options granted to directors vest immediately. During the year ended December 31, 2013, the Company also issued options to purchase less than 0.1 million shares of common stock to non-employees. The assumptions used to estimate the fair value of options granted to non-employees at the date of grant were materially consistent with those used for employee and director grants. The Company did not grant any options to purchase common stock to non-employees during the years ended December 31, 2015 or 2014.

The Company recognized stock-based compensation expense as follows:


	Years ended December 31,
(in thousands)	2015		2014		2013
Employee awards:
Research and development	$	8,271	$	6,864	$	5,954
General and administrative		7,022		6,065		4,808

Stock-based compensation for employee awards		15,293		12,929		10,762
Stock-based compensation for non-employee awards		58		268		(29	)

Total stock-based compensation	$	15,351	$	13,197	$	10,733

The fair value of stock options granted to employees during the years ended December 31, 2015, 2014 and 2013 was estimated at the date of grant using the following assumptions:


	Years ended December 31,
	2015	2014	2013
Risk-free interest rate	1.5 - 1.8%	1.6 - 2.0%	0.1 - 1.9%
Expected dividend yield	0%	0%	0%
Expected term	5.0 - 5.9 years	5.0 - 5.9 years	5.3 - 5.9 years
Expected volatility	66 - 67%	64 - 72%	67 - 70%

The Company uses the simplified method to calculate the expected term, as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate expected term. The computation of expected volatility is based on the historical volatility of comparable companies from a representative peer group selected based on industry and market capitalization. The risk-free interest rate is based on a treasury instrument whose term is consistent with the expected life of the stock options. Management estimates expected forfeitures based on historical experience and recognizes compensation costs only for those equity awards expected to vest.

The following table summarizes stock option activity during the year ended December 31, 2015:


(in thousands, except per share amounts)	Shares			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2014		19,556		$	4.47		6.17	$	133,599
Granted		3,720		$	9.63
Exercised		(3,606	)	$	2.75
Forfeited		(459	)	$	7.36

Outstanding at December 31, 2015		19,211		$	5.72		6.24	$	47,963
Vested and expected to vest at December 31, 2015		18,923		$	5.68		6.20	$	47,818
Exercisable at December 31, 2015		14,783		$	5.01		5.48	$	44,173

The weighted-average grant date fair value of stock options granted during the years ended December 31, 2015, 2014 and 2013 was $5.80, $3.41 and $3.59, respectively.

The aggregate intrinsic value was calculated as the difference between the exercise price of the stock options and the fair value of the underlying common stock. The aggregate intrinsic value of options exercised during the years ended December 31, 2015, 2014 and 2013 was $30.9 million, $19.8 million and $2.7 million, respectively.

As of December 31, 2015, there was $18.3 million of total unrecognized compensation cost related to unvested employee stock awards. As of December 31, 2015, the Company expects to recognize those costs over a weighted average period of approximately 1.8 years.

Income Taxes

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Income Taxes

16. Income Taxes

As a result of losses incurred, the Company did not provide for any income taxes in the years ended December 31, 2015, 2014 or 2013. A reconciliation of the Company’s effective tax rate to the statutory federal income tax rate is as follows:


	Years Ended December 31,
	2015			2014			2013
Federal income tax at statutory federal rate		35.0	%		35.0	%		35.0	%
State taxes		1.0			3.1			4.3
Permanent differences		(6.4	)		(9.1	)		(2.0	)
Stock-based compensation		(1.3	)		(1.7	)		(0.6	)
Tax credits		21.3			30.5			12.4
Foreign rate differential		—			(2.3	)		(2.8	)
Change in deferred state tax rate		(2.3	)		—			—
Other		(0.5	)		4.5			(1.5	)
Change in valuation allowance		(46.8	)		(60.0	)		(44.8	)

		—	%		—	%		—	%

During the year ended December 31, 2014, the Company recorded a deferred tax liability related to the embedded conversion option of the Convertible Notes though equity. This deferred tax liability is reflected in the deferred tax table below, but is appropriately excluded from the effective tax rate.

Temporary differences that give rise to significant net deferred tax assets as of December 31, 2015 and 2014 are as follows:


(in thousands)	December 31, 2015			December 31, 2014
Deferred tax assets
Net operating losses	$	182,992		$	160,333
Capitalized research and development expenses		21,444			30,929
Credit carryforwards		93,113			62,362
Depreciation		2,128			2,579
Deferred compensation		11,664			10,682
Accrued expenses		1,807			12
Deferred revenue		10,999			960
Other temporary differences		17,235			9,195

Total gross deferred tax asset		341,382			277,052
Valuation allowance		(326,577	)		(257,489	)

Net deferred tax asset		14,805			19,563
Deferred tax liabilities
Intangible assets		(2,667	)		(3,106	)
Debt discount		(12,138	)		(16,457	)

Net deferred taxes	$	—		$	—

The Company concluded that there are no significant uncertain tax positions requiring recognition in the consolidated financial statements. The Company’s evaluation was performed for the tax years ended December 31, 2012 through 2015, the tax years which remain subject to examination by major tax jurisdictions as of December 31, 2015. However, to the extent the Company utilizes net operating losses from years prior to 2011, the statute remains open to the extent of the net operating losses utilized. The Company’s policy is to recognize interest and penalties for uncertain tax positions as a component of income tax expense. The Company has not recognized any interest and penalties historically through December 31, 2015.

At December 31, 2015, the Company had net operating loss carryforwards for federal and state income tax purposes of $509.8 million and $356.9 million, respectively. Included in the federal and state net operating loss carryforwards is approximately $36.5 million and $24.7 million, respectively, of deduction related to the exercise of stock options. This amount represents an excess tax benefit, which will be realized when it results in reduction of cash taxes in accordance with ASC 718. This excess tax benefit will be directly credited to additional paid-in capital when it is realized. The Company’s existing federal and state net operating loss carryforwards will expire in years through 2035. The Company also has available research and development credits for federal and state income tax purposes of approximately $23.7 million and $9.6 million, respectively. The federal and state research and development credits will begin to expire in 2022 and 2026, respectively. As of December 31, 2015, the Company also had available investment tax credits for state income tax purposes of $0.8 million, which will expire in years through 2018 if unused. In addition, the Company has federal orphan drug credits of $62.7 million which begin to expire in 2031. The Company has evaluated the positive and negative evidence bearing upon the realizability of its deferred tax assets, which are comprised principally of net operating loss carryforwards, deferred revenue and capitalized research and development expenses. Under the applicable accounting standards, the Company has considered its history of losses and concluded that it is more likely than not that the Company will not recognize the benefits of federal and state deferred tax assets. Accordingly, the Company has established a full valuation allowance against the deferred tax assets.

Utilization of the net operating loss and research and development credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986, as amended (the “Internal Revenue Code”), due to ownership change limitations that have occurred previously or that could occur in the future. These ownership changes may limit the amount of net operating loss and research and development credit carryforwards that can be utilized annually to offset future taxable income and tax. The Company has not currently completed an evaluation of ownership changes through December 31, 2015 to assess whether utilization of the Company’s net operating loss or research and development credit carryforwards would be subject to an annual limitation under Section 382 of the Internal Revenue Code. To the extent an ownership change occurs in the future, the net operating loss and credit carryforwards may be subject to limitation.

The Company has not yet conducted a study of its domestic research and development credit carryforwards and orphan drug credits. This study may result in an increase or decrease to the Company’s credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s credits, and if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. As a result, there would be no impact to the consolidated statements of operations and comprehensive loss or consolidated statements of cash flows if an adjustment were required.

The change in the valuation allowance against the deferred tax assets in the years ended December 31, 2015, 2014 and 2013 was as follows:


(in thousands)	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
December 31, 2013	$	169,651	$	37,653	$	—	$	207,304
December 31, 2014		207,304		50,185		—		257,489
December 31, 2015		257,489		69,088		—		326,577

Commitments and Contingencies

12 Months Ended

Dec. 31, 2015

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

17. Commitments and Contingencies

Operating Leases

The Company leases its office, laboratory and manufacturing space under non-cancelable operating leases. Total rent expense under these operating leases was $7.4 million, $5.9 million and $5.5 million for the years ended December 31, 2015, 2014 and 2013, respectively.

During August 2012, the Company entered into an Indenture of Lease (the “Amended Lease”), which amended and restated its facility lease, and agreed to occupy approximately a total of 109,000 square feet, all of which is leased until June 30, 2019. In March and September 2013, the Company entered into facility lease amendments that are co-terminus with the existing lease. As part of the Amended Lease and subsequent amendments, the landlord agreed to reimburse the Company for a portion of tenant improvements made to the facility, up to approximately $8.2 million. On February 23, 2015 and July 22, 2015, the Company entered into amendments to its facility lease. These lease amendments provide an additional 45,463 square feet of leased space in total at the Company’s current facility with a termination date of June 30, 2019, which is co-terminous with the Company’s existing lease. As a result of these amendments, the Company agreed to additional lease payments totaling approximately $9.3 million through 2019. In addition, under the terms of the amendments, the landlord agreed to provide the Company with an aggregate leasehold improvement allowance of up to $1.3 million.

As of both December 31, 2015 and 2014, the Company has received $8.2 million, of these tenant improvement reimbursements, with the remaining reimbursable tenant improvements recorded within other current assets on the consolidated balance sheets. Tenant improvements recorded in deferred rent are amortized over the term of the lease as reductions to rent expense. The Amended Lease expires on June 30, 2019. The Company retains an option to renew the Amended Lease with respect to all of the leased space for an additional period of either one or five years.

Future minimum lease payments under non-cancelable operating leases at December 31, 2015 are as follows:


Years ended December 31,	(in thousands)
2016	$	7,543
2017		7,690
2018		7,846
2019		3,953

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2015
Related Party Transactions [Abstract]
Related Party Transactions	18. Related Party Transactions Related parties of the Company held approximately 6% of the outstanding shares of Silver Creek Series A preferred stock as of December 31, 2014. Related parties of the Company held approximately 7% of the outstanding shares of Silver Creek Series A and Series B preferred stock as of December 31, 2015.

- Definition

The entire disclosure for related party transactions. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.

+ References + Details

Selected Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data (Unaudited)

20. Selected Quarterly Financial Data (Unaudited)

The following table contains quarterly financial information for 2015 and 2014. The Company believes that the following information reflects all normal recurring adjustments necessary for a fair statement of the information for the periods presented. The operating results for any quarter are not necessarily indicative of results for any future period.


	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	(in thousands, except per share data)
2015
Product revenues, net	$	—		$	—		$	—		$	4,328
License and collaboration revenues		14,842			36,558			16,440			17,090
Cost of product revenues		—			—			—			46
Research and development expenses		35,679			42,806			37,763			44,740
Selling, general and administrative expenses		9,189			12,315			16,956			19,335
Net loss		(34,432	)		(22,901	)		(42,386	)		(48,068	)
Net loss attributable to Merrimack Pharmaceuticals, Inc.		(34,759	)		(22,778	)		(42,594	)		(47,826	)
Net loss per share available to common stockholders—basic and diluted	$	(0.32	)	$	(0.21	)	$	(0.38	)	$	(0.41	)


	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	(in thousands, except per share data)
2014
License and collaboration revenues	$	13,034		$	27,815		$	28,002		$	33,905
Research and development expenses		30,324			33,795			43,632			30,744
Selling, general and administrative expenses		6,224			7,921			8,095			8,277
Net loss		(27,754	)		(18,290	)		(28,038	)		(9,477	)
Net loss attributable to Merrimack Pharmaceuticals, Inc.		(27,585	)		(18,109	)		(27,901	)		(9,696	)
Net loss per share available to common stockholders—basic and diluted	$	(0.27	)	$	(0.17	)	$	(0.27	)	$	(0.09	)

Nature of the Business and Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2015

Accounting Policies [Abstract]

Segment Information

Segment Information

Basis of Presentation and Consolidation

Basis of Presentation and Consolidation

Use of Estimates

Use of Estimates

Cash, Cash Equivalents and Restricted Cash

Cash, Cash Equivalents and Restricted Cash

Marketable Securities

Marketable Securities

Inventory

Inventory

Property and Equipment

Property and Equipment


Asset classification		Estimated useful life (in years)
Lab equipment		3 - 7
IT equipment		3 - 7
Leaseholds improvements		Lesser of useful life or lease term
Furniture and fixtures		3 - 7

Goodwill and Intangible Assets

Goodwill and Intangible Assets

Accrued Expenses

Accrued Expenses

•

fees due to contract research organizations in connection with preclinical and toxicology studies and clinical trials;

•

fees paid to investigative sites in connection with clinical trials; and

•

professional service fees.

Non-Controlling Interest

Non-Controlling Interest

Revenue Recognition

Revenue Recognition

Product Revenues, Net

Product revenue reserves and allowances that reduce gross revenue are categorized as follows:

License and Collaboration Revenues

Royalty revenue will be recognized upon the sale of the related products provided the Company has no remaining performance obligations under the arrangement.

Research and Development Expenses

Research and Development Expenses

Advertising Expenses

Advertising Expenses

Stock-Based Compensation

Stock-Based Compensation

Comprehensive Income (Loss)

Comprehensive Income (Loss)

Other Income and Expense

Other Income and Expense

The Company records gains and losses on federal and state sponsored tax incentives and other income or expense-related items in other income and expense.

Income Taxes

Income Taxes

Concentration of Credit Risk

Concentration of Credit Risk


	Years Ended December 31,
	2015	2014	2013
Baxalta	93%	10%	—
Sanofi	—	90%	98%


	December 31,
	2015	2014
Baxalta	29%	49%
Sanofi	—	50%
AmerisourceBergen Corporation	29%	—
McKesson Corporation	25%	—
Cardinal Health, Inc.	16%	—

Recent Accounting Pronouncements

Recent Accounting Pronouncements

Nature of the Business and Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2015

Accounting Policies [Abstract]

Schedule of Estimated Useful Lives of Property and Equipment Including Leasehold Improvements


Asset classification		Estimated useful life (in years)
Lab equipment		3 - 7
IT equipment		3 - 7
Leaseholds improvements		Lesser of useful life or lease term
Furniture and fixtures		3 - 7

Schedules of Concentration of Risk by Risk Factor


	Years Ended December 31,
	2015	2014	2013
Baxalta	93%	10%	—
Sanofi	—	90%	98%


	December 31,
	2015	2014
Baxalta	29%	49%
Sanofi	—	50%
AmerisourceBergen Corporation	29%	—
McKesson Corporation	25%	—
Cardinal Health, Inc.	16%	—

Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2015

Investments, Debt and Equity Securities [Abstract]

Schedule of Marketable Securities

As of December 31, 2015, the Company maintained no marketable securities. Marketable securities as of December 31, 2014 consisted of the following, all of which were classified as available-for-sale:


	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
December 31, 2014:
Commercial paper	$	6,493	$	—	$	(2	)	$	6,491
Corporate debt securities		81,921		—		(72	)		81,849

Total	$	88,414	$	—	$	(74	)	$	88,340

Net Loss Per Common Share (Tables)

12 Months Ended

Dec. 31, 2015

Earnings Per Share [Abstract]

Schedule of Securities Excluded from Computation of Diluted Loss Per Share

Securities excluded from the calculation of diluted loss per share are shown in the chart below:


	Years ended December 31,
(in thousands)	2015		2014		2013
Common stock warrants		—		2,381		2,777
Outstanding options to purchase common stock		19,211		19,567		20,107
Conversion of the Convertible Notes		25,000		25,000		25,000

Product Revenue Reserves and Allowances (Tables)

12 Months Ended

Dec. 31, 2015

Text Block [Abstract]

Summary of Product Revenue Reserve and Allowance Categories

The following table summarizes activity in each of the product revenue reserve and allowance categories for the year ended December 31, 2015:


(in thousands)	Trade Allowances			Rebates and Chargeback Discounts			Product Returns		Other Incentives		Total
Beginning balance	$	—		$	—		$	—	$	—	$	—
Provisions related to sales in the current year		153			456			32		8		649
Adjustments related to sales in the prior year		—			—			—		—		—
Credits and payments made		(15	)		(94	)		—		—		(109	)

Ending balance	$	138		$	362		$	32	$	8	$	540

License and Collaboration Agreements (Tables)

12 Months Ended

Dec. 31, 2015

Baxalta [Member]

Schedule of Revenue Recognized and Assets and Liabilities under Collaborative Arrangements

During the years ended December 31, 2015 and 2014, the Company recognized revenue based on the following components of the Baxalta Agreement:


	Year Ended December 31,		Year Ended December 31,
(in thousands)	2015		2014
Proportional performance revenue recognition model	$	64,930	$	10,460
Substantive milestones		20,000		—

Total	$	84,930	$	10,460

As of December 31, 2015 and 2014, the Company maintained the following assets and liabilities related to the Baxalta Agreement:


(in thousands)	December 31, 2015		December 31, 2014
Accounts receivable, billed	$	1,336	$	—
Accounts receivable, unbilled		626		1,615
Deferred revenue		97,365		91,156

Sanofi [Member]

Schedule of Revenue Recognized and Assets and Liabilities under Collaborative Arrangements

During the years ended December 31, 2014 and 2013, the Company recognized revenue based on the following components of the Sanofi agreement:


	Years ended December 31,
(in thousands)	2014		2013
Upfront payment	$	39,306	$	5,000
Milestone payment		16,377		2,083
Development services		18,904		36,283
Manufacturing services and other		17,709		3,867

Total	$	92,296	$	47,233


(in thousands)	December 31, 2014
Accounts receivable, billed	$	369
Accounts receivable, unbilled		1,282
Deferred revenues		—

Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2015

Fair Value Disclosures [Abstract]

Schedule of Assets Measured at Fair Value on a Recurring Basis

The following tables show assets measured at fair value on a recurring basis as of December 31, 2015 and 2014 and the input categories associated with those assets:


As of December 31, 2015 (in thousands)	Level 1		Level 2		Level 3
Assets:
Cash equivalents – money market funds	$	704	$	—	$	—
Marketable securities – commercial paper		—		—		—
Marketable securities – corporate debt securities		—		—		—

As of December 31, 2014 (in thousands)	Level 1		Level 2		Level 3
Assets:
Cash equivalents – money market funds	$	33,199	$	—	$	—
Marketable securities – commercial paper		—		6,491		—
Marketable securities – corporate debt securities		—		81,849		—

Goodwill and Intangible Assets, Net (Tables)

12 Months Ended

Dec. 31, 2015

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Changes in the Carrying Value of Goodwill, IPR&D and Intangible Assets

Changes in the carrying value of the nano-carrier technology intangible asset, the ONIVYDE intangible asset, IPR&D and goodwill for the years ended December 31, 2015 and 2014 were as follows:


(in thousands)	Nano-carrier technology intangible asset			ONIVYDE intangible asset			IPR&D			Goodwill
Balance, December 31, 2013	$	1,845		$	—		$	6,200		$	3,605
Amortization		(320	)		—			—			—

Balance, December 31, 2014		1,525			—			6,200			3,605
Reclassification of IPR&D to definite-lived intangible assets		—			3,400			(3,400	)		—
Amortization		(320	)		(50	)		—			—

Balance, December 31, 2015	$	1,205		$	3,350		$	2,800		$	3,605

Schedule of Expected Amortization Expense for Intangible Assets for the Next Five-Year Period

Amortization expense is expected to be as follows for the next five-year period:


Years Ended December 31,	(in thousands)
2016	$	578
2017		578
2018		578
2019		503
2020		258

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2015

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment, Net

Property and equipment, net as of December 31, 2015 and 2014 consisted of the following:


	December 31,
(in thousands)	2015			2014
Lab equipment	$	19,305		$	16,214
IT equipment		7,742			3,113
Leasehold improvements		21,026			18,219
Furniture and fixtures		910			624
Construction in process		2,243			472

Total property and equipment, gross		51,226			38,642
Less: Accumulated depreciation		(29,311	)		(24,140	)

Total property and equipment, net	$	21,915		$	14,502

Accounts Payables, Accrued Expenses and Other (Tables)

12 Months Ended

Dec. 31, 2015

Payables and Accruals [Abstract]

Schedule of Accounts Payable, Accrued Expenses and Other

Accounts payable, accrued expenses and other as of December 31, 2015 and 2014 consisted of the following:


	December 31,
(in thousands)	2015		2014
Accounts payable	$	5,049	$	2,510
Accrued goods and services		14,295		17,481
Accrued clinical trial costs		12,764		7,637
Accrued drug purchase costs		7,460		—
Accrued payroll and related benefits		9,009		6,166
Accrued interest		3,041		2,956
Accrued dividends payable		19		19
Deferred tax incentives		445		467

Total accounts payable, accrued expenses and other	$	52,082	$	37,236

Borrowings (Tables)

12 Months Ended

Dec. 31, 2015

Debt Disclosure [Abstract]

Schedule of Future Minimum Payments under the Loans Payable

Future minimum payments under outstanding borrowings as of December 31, 2015 are as follows:


(in thousands)	Convertible Notes			2022 Notes
2016	$	5,625		$	19,734
2017		5,625			20,125
2018		5,625			20,125
2019		5,625			62,617
2020 and thereafter		130,625			157,664

Total	$	153,125		$	280,265
Less interest		(28,125	)		(105,265	)
Less unamortized discount		(36,505	)		(5,840	)
Less current portion		—			—

Long-term debt, net of current portion	$	88,495		$	169,160

Stock Warrants (Tables)

12 Months Ended

Dec. 31, 2015

Text Block [Abstract]

Schedule of Common Stock Warrant Activity of the Company

The following is a description of the common stock warrant activity of the Company:


(in thousands, except per share amounts)	Warrants for the Purchase of Common Stock			Weighted Average Exercise Price
Balance—December 31, 2012		2,842		$	3.05
Exercised		(65	)	$	2.82

Balance—December 31, 2013		2,777		$	3.05
Exercised		(396	)	$	3.38

Balance—December 31, 2014		2,381		$	3.00
Exercised		(2,355	)	$	3.00
Cancelled		(26	)	$	3.00

Balance—December 31, 2015		—		$	—

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Recognized Stock-Based Compensation Expense

The Company recognized stock-based compensation expense as follows:


	Years ended December 31,
(in thousands)	2015		2014		2013
Employee awards:
Research and development	$	8,271	$	6,864	$	5,954
General and administrative		7,022		6,065		4,808

Stock-based compensation for employee awards		15,293		12,929		10,762
Stock-based compensation for non-employee awards		58		268		(29	)

Total stock-based compensation	$	15,351	$	13,197	$	10,733

Schedule of Assumptions Used to Calculate Fair Value of Options Granted to Employees

The fair value of stock options granted to employees during the years ended December 31, 2015, 2014 and 2013 was estimated at the date of grant using the following assumptions:


	Years ended December 31,
	2015	2014	2013
Risk-free interest rate	1.5 - 1.8%	1.6 - 2.0%	0.1 - 1.9%
Expected dividend yield	0%	0%	0%
Expected term	5.0 - 5.9 years	5.0 - 5.9 years	5.3 - 5.9 years
Expected volatility	66 - 67%	64 - 72%	67 - 70%

Summary of Stock Option Activity

The following table summarizes stock option activity during the year ended December 31, 2015:


(in thousands, except per share amounts)	Shares			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding at December 31, 2014		19,556		$	4.47		6.17	$	133,599
Granted		3,720		$	9.63
Exercised		(3,606	)	$	2.75
Forfeited		(459	)	$	7.36

Outstanding at December 31, 2015		19,211		$	5.72		6.24	$	47,963
Vested and expected to vest at December 31, 2015		18,923		$	5.68		6.20	$	47,818
Exercisable at December 31, 2015		14,783		$	5.01		5.48	$	44,173

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of the Company's Effective Tax Rate to the Statutory Federal Income Tax Rate

A reconciliation of the Company’s effective tax rate to the statutory federal income tax rate is as follows:


	Years Ended December 31,
	2015			2014			2013
Federal income tax at statutory federal rate		35.0	%		35.0	%		35.0	%
State taxes		1.0			3.1			4.3
Permanent differences		(6.4	)		(9.1	)		(2.0	)
Stock-based compensation		(1.3	)		(1.7	)		(0.6	)
Tax credits		21.3			30.5			12.4
Foreign rate differential		—			(2.3	)		(2.8	)
Change in deferred state tax rate		(2.3	)		—			—
Other		(0.5	)		4.5			(1.5	)
Change in valuation allowance		(46.8	)		(60.0	)		(44.8	)

		—	%		—	%		—	%

Schedule of Temporary Differences That Give Rise to Significant Net Deferred Tax Assets

Temporary differences that give rise to significant net deferred tax assets as of December 31, 2015 and 2014 are as follows:


(in thousands)	December 31, 2015			December 31, 2014
Deferred tax assets
Net operating losses	$	182,992		$	160,333
Capitalized research and development expenses		21,444			30,929
Credit carryforwards		93,113			62,362
Depreciation		2,128			2,579
Deferred compensation		11,664			10,682
Accrued expenses		1,807			12
Deferred revenue		10,999			960
Other temporary differences		17,235			9,195

Total gross deferred tax asset		341,382			277,052
Valuation allowance		(326,577	)		(257,489	)

Net deferred tax asset		14,805			19,563
Deferred tax liabilities
Intangible assets		(2,667	)		(3,106	)
Debt discount		(12,138	)		(16,457	)

Net deferred taxes	$	—		$	—

Schedule of Changes in the Valuation Allowance

The change in the valuation allowance against the deferred tax assets in the years ended December 31, 2015, 2014 and 2013 was as follows:


(in thousands)	Balance at Beginning of Period		Additions		Deductions		Balance at End of Period
December 31, 2013	$	169,651	$	37,653	$	—	$	207,304
December 31, 2014		207,304		50,185		—		257,489
December 31, 2015		257,489		69,088		—		326,577

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2015

Commitments and Contingencies Disclosure [Abstract]

Schedule of Future Minimum Lease Payments Under Non-cancelable Operating Leases

Future minimum lease payments under non-cancelable operating leases at December 31, 2015 are as follows:


Years ended December 31,	(in thousands)
2016	$	7,543
2017		7,690
2018		7,846
2019		3,953

Selected Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information


	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	(in thousands, except per share data)
2015
Product revenues, net	$	—		$	—		$	—		$	4,328
License and collaboration revenues		14,842			36,558			16,440			17,090
Cost of product revenues		—			—			—			46
Research and development expenses		35,679			42,806			37,763			44,740
Selling, general and administrative expenses		9,189			12,315			16,956			19,335
Net loss		(34,432	)		(22,901	)		(42,386	)		(48,068	)
Net loss attributable to Merrimack Pharmaceuticals, Inc.		(34,759	)		(22,778	)		(42,594	)		(47,826	)
Net loss per share available to common stockholders—basic and diluted	$	(0.32	)	$	(0.21	)	$	(0.38	)	$	(0.41	)


	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
	(in thousands, except per share data)
2014
License and collaboration revenues	$	13,034		$	27,815		$	28,002		$	33,905
Research and development expenses		30,324			33,795			43,632			30,744
Selling, general and administrative expenses		6,224			7,921			8,095			8,277
Net loss		(27,754	)		(18,290	)		(28,038	)		(9,477	)
Net loss attributable to Merrimack Pharmaceuticals, Inc.		(27,585	)		(18,109	)		(27,901	)		(9,696	)
Net loss per share available to common stockholders—basic and diluted	$	(0.27	)	$	(0.17	)	$	(0.27	)	$	(0.09	)

Nature of the Business and Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($) Segment Region	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments \| Segment		1
Number of geographic regions \| Region		1
Original maturities		Three months or less
Restricted cash		$ 685,000	$ 685,000
Impairment of goodwill	$ 0
Advertising expenses		$ 1,000,000
Performance period		5 years
Tax incentive awarded		$ 3,800,000
State research and development tax credits monetized		3,400,000
Amount of benefit recognized		$ 700,000	400,000	$ 300,000
Short-term debt issuance cost			100,000
Long-term debt issuance cost			$ 100,000
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Expected remaining maturities period of marketable securities classified as available-for-sale		3 months

Nature of the Business and Summary of Significant Accounting Policies - Schedule of Estimated Useful Lives of Property and Equipment Including Leasehold Improvements (Detail)	12 Months Ended
	Dec. 31, 2015
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	Lesser of useful life or lease term
Minimum [Member] \| Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Minimum [Member] \| IT Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Minimum [Member] \| Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Maximum [Member] \| Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	7 years
Maximum [Member] \| IT Equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	7 years
Maximum [Member] \| Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	7 years

Nature of the Business and Summary of Significant Accounting Policies - Schedules of Concentration of Risk by Risk Factor - Gross Sales Revenue (Detail) - Sales Revenue, Net [Member] - Customer Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Baxalta [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross revenue	93.00%	10.00%
Sanofi [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross revenue		90.00%	98.00%

Nature of the Business and Summary of Significant Accounting Policies - Schedules of Concentration of Risk by Risk Factor - Gross Accounts Receivable (Detail) - Accounts Receivable [Member] - Credit Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Baxalta [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross accounts receivable	29.00%	49.00%
Sanofi [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross accounts receivable		50.00%
Amerisource Bergen Corporation [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross accounts receivable	29.00%
Mckesson Corporation [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross accounts receivable	25.00%
Cardinal Health Inc [Member]
Concentration Risk [Line Items]
Customer's accounted for more than 10% percent gross accounts receivable	16.00%

Marketable Securities - Additional Information (Detail)	12 Months Ended
Marketable Securities - Additional Information (Detail)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) Security	Dec. 31, 2013 USD ($)
Amortized Cost and Fair Value Debt Securities [Abstract]
Marketable securities	$ 0
Aggregate fair value		$ 88,400,000
Number of securities in unrealized loss position for less than 12 months \| Security		35
Other-than-temporary-impairment investments		$ 0
Realized gains (losses) on sale of available-for-sale securities	$ 0	$ 0	$ 0

Marketable Securities - Schedule of Marketable Securities (Detail) $ in Thousands	Dec. 31, 2014 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 88,414
Unrealized Gains	0
Unrealized Losses	(74)
Fair Value	88,340
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,493
Unrealized Gains	0
Unrealized Losses	(2)
Fair Value	6,491
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	81,921
Unrealized Gains	0
Unrealized Losses	(72)
Fair Value	$ 81,849

Net Loss Per Common Share - Additional Information (Detail) - Convertible Notes [Member] - USD ($) $ in Millions	1 Months Ended
	Jul. 31, 2013	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Aggregate principal amount	$ 125.0
Interest rate (as a percent)	4.50%	4.50%

Net Loss Per Common Share - Schedule of Securities Excluded from Computation of Diluted Loss Per Share (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common Stock Warrants [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted loss per share		2,381	2,777
Stock Compensation Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted loss per share	19,211	19,567	20,107
Conversion of the Convertible Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted loss per share	25,000	25,000	25,000

Product Revenue Reserves and Allowances - Summary of Product Revenue Reserve and Allowance Categories (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)
Valuation and Qualifying Accounts Disclosure [Line Items]
Provisions related to sales in the current year	$ 649
Adjustments related to sales in the prior year	0
Credits and payments made	(109)
Ending balance	540
Trade Allowances [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Provisions related to sales in the current year	153
Adjustments related to sales in the prior year	0
Credits and payments made	(15)
Ending balance	138
Rebates and Chargeback Discounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Provisions related to sales in the current year	456
Adjustments related to sales in the prior year	0
Credits and payments made	(94)
Ending balance	362
Product Returns [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Provisions related to sales in the current year	32
Adjustments related to sales in the prior year	0
Ending balance	32
Other Incentives [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Provisions related to sales in the current year	8
Adjustments related to sales in the prior year	0
Ending balance	$ 8

License and Collaboration Agreements - Additional Information (Detail) - USD ($)					1 Months Ended						3 Months Ended								12 Months Ended			25 Months Ended	36 Months Ended
	Sep. 23, 2014	Nov. 25, 2013	May. 05, 2011	Nov. 10, 2009	Oct. 31, 2015	Aug. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2015	Sep. 30, 2014	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2012
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue, current											$ 50,137,000				$ 59,275,000				$ 50,137,000	$ 59,275,000		$ 50,137,000
Agreement termination scheduled date																			Dec. 17, 2014
License and collaboration revenues											17,090,000	$ 16,440,000	$ 36,558,000	$ 14,842,000	33,905,000	$ 28,002,000	$ 27,815,000	$ 13,034,000	$ 84,930,000	102,756,000	$ 47,786,000
Assets maintained related to Sanofi Agreement											234,880,000				158,506,000				234,880,000	158,506,000		234,880,000
Liabilities maintained related to Sanofi Agreement											418,569,000				260,577,000				418,569,000	260,577,000		418,569,000
Research and development expenses											44,740,000	$ 37,763,000	42,806,000	$ 35,679,000	30,744,000	$ 43,632,000	$ 33,795,000	$ 30,324,000	$ 160,988,000	138,495,000	147,139,000
Baxalta [Member] \| License and Collaboration Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront license fee received										$ 100,000,000
Royalty for improved products																			The Company is also entitled to tiered, escalating royalties ranging from sub-teen double-digits to low twenties percentages of net sales of MM-398 in the Licensed Territory.
Notice period of termination																			180 days
Revenue recognized related to a substantive milestone payment					$ 47,500,000	$ 15,000,000							$ 20,000,000
Deferred revenue											97,365,000				91,156,000				$ 97,365,000	91,156,000		97,365,000
Deferred revenue, current											50,100,000								50,100,000			50,100,000
License and collaboration revenues																			84,930,000	10,460,000
Baxalta [Member] \| License and Collaboration Agreements [Member] \| Sales Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum amount of milestone payments that can be received	$ 250,000,000
Baxalta [Member] \| License and Collaboration Agreements [Member] \| Research and Development Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum amount of milestone payments that can be received	100,000,000
Baxalta [Member] \| License and Collaboration Agreements [Member] \| Regulatory Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone license fee received																			20,000,000
Maximum amount of milestone payments that can be received	520,000,000
Baxalta [Member] \| License and Collaboration Agreements [Member] \| Clinical Trials in Pancreatic Cancer [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone license fee received																			62,500,000
Collaboration agreement costs																			98,800,000
Baxalta [Member] \| Non-Substantive Collaborative Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone license fee received																			62,500,000
Milestone license fee	90,000,000
Baxalta [Member] \| Substantive Collaborative Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone license fee received																			20,000,000
Milestone license fee	$ 530,000,000
Sanofi [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront license fee received				$ 60,000,000
Milestone license fee received																							$ 25,000,000
Expected development period from the effective date of agreement				12 years
License and collaboration revenues																			0
Assets maintained related to Sanofi Agreement											0								0			0
Liabilities maintained related to Sanofi Agreement											0								0			0
Sanofi [Member] \| License and Collaboration Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
License and collaboration revenues																				92,296,000	47,233,000
Recognized revenue related to excess spending																				5,800,000
Spending in excess of budget																					10,100,000
PharmaEngine [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront license fees paid			$ 10,000,000
PharmaEngine [Member] \| Development and Regulatory Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum milestone payment obligation			80,000,000
PharmaEngine [Member] \| Sales Milestone [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum milestone payment obligation			$ 130,000,000
PharmaEngine [Member] \| License and Collaboration Agreements [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment							$ 11,000,000			$ 7,000,000
Research and development expenses																			$ 11,400,000	12,600,000	$ 1,500,000
PharmaEngine [Member] \| License and Collaboration Agreements [Member] \| New Drug Application [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone payment								$ 5,000,000
Actavis [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Maximum amount of milestone payments that can be received		$ 15,100,000
Notice period of termination																			90 days
Collaborative arrangement gross payments received																						3,900,000
Aggregate milestone payments eligible to receive, decrease									$ 400,000
Agreement expiration term respect to each product																			10 years
Additional renewal term																			2 years
Milestones and development expenses											$ 4,000,000				$ 3,800,000				$ 4,000,000	$ 3,800,000		$ 4,000,000
Expected revenue recognition period begins after first sale of applicable product																			10 years

License and Collaboration Agreements - Schedule of Revenue Recognized and Assets and Liabilities under Collaborative Arrangements (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total	$ 17,090,000	$ 16,440,000	$ 36,558,000	$ 14,842,000	$ 33,905,000	$ 28,002,000	$ 27,815,000	$ 13,034,000	$ 84,930,000	$ 102,756,000	$ 47,786,000
Sanofi [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total									0
License and Collaboration Agreements [Member] \| Baxalta [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proportional performance revenue recognition model									64,930,000	10,460,000
Substantive milestones									20,000,000
Total									84,930,000	10,460,000
Accounts receivable, billed	1,336,000								1,336,000
Accounts receivable, unbilled	626,000				1,615,000				626,000	1,615,000
Deferred revenue	$ 97,365,000				91,156,000				$ 97,365,000	91,156,000
License and Collaboration Agreements [Member] \| Sanofi [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment										39,306,000	5,000,000
Milestone payment										16,377,000	2,083,000
Development services										18,904,000	36,283,000
Manufacturing services and other										17,709,000	3,867,000
Total										92,296,000	$ 47,233,000
Accounts receivable, billed					369,000					369,000
Accounts receivable, unbilled					$ 1,282,000					$ 1,282,000

Fair Value of Financial Instruments - Schedule of Assets Measured at Fair Value on a Recurring Basis (Detail) - Recurring Basis [Member] - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Level 1 [Member] \| Money Market Funds [Member]
Assets:
Cash equivalents	$ 704	$ 33,199
Level 2 [Member] \| Commercial Paper [Member]
Assets:
Marketable securities		6,491
Level 2 [Member] \| Corporate Debt Securities [Member]
Assets:
Marketable securities		$ 81,849

Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 22, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Asset impairment charges	$ 0	$ 0	$ 0
Transfers between fair value measurement levels	0	0
Non-recurring fair value measurements	0	0
Recurring Basis [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Liabilities measured at fair value	0	$ 0
Senior Convertible Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Aggregate principal amount of loan	125,000,000
Carrying value of debt	88,500,000
Senior Convertible Notes [Member] \| Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of debt	184,600,000
2022 Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Aggregate principal amount of loan				$ 175,000,000
Fair value of debt	175,000,000
Carrying value of debt	169,200,000
Private placement	$ 175,000,000
Interest rate (as a percent)				11.50%
2022 Notes [Member] \| Private Placement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Interest rate (as a percent)	11.50%

Consolidated Subsidiaries - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Feb. 28, 2013	Dec. 31, 2012
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Outstanding borrowings and accrued interest		$ 1,044	$ 2,603
Preferred stock value, per share	$ 0.01	$ 0.01
Preferred stock issued and sold	0	0
Proceeds from issuance of preferred stock after deducting issuance costs	$ 2,083
Total assets of consolidated subsidiaries	234,880	$ 158,506
Total liabilities of consolidated subsidiaries	418,569	260,577
Silver Creek Series B Preferred Stock [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Non-controlling interest increased	$ 1,188
Silver Creek [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Acquisition date	Aug. 20, 2010
Non-controlling interest increased		$ 400	$ 800
Ownership interest (as a percent)		60.00%	64.00%		74.00%
Total assets of consolidated subsidiaries	$ 800	$ 300
Total liabilities of consolidated subsidiaries	200	200
Unrestricted cash and cash equivalents balance	$ 700	300
Silver Creek [Member] \| Silver Creek Convertible Note [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Aggregate principal amounts		$ 1,000	$ 600	$ 300	$ 1,600
Outstanding borrowings and accrued interest			$ 2,600
Silver Creek [Member] \| Silver Creek Series B Preferred Stock [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Preferred stock value, per share	$ 1.35
Non-controlling interest increased	$ 900
Preferred stock issued and sold	1,600
Silver Creek [Member] \| Series A and B Preferred Stock [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Ownership interest (as a percent)	56.00%	60.00%
Non-controlling interest	$ 200	$ 100
Silver Creek [Member] \| Series A Preferred Stock [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Preferred stock value, per share		$ 1.00	$ 1.00

Goodwill and Intangible Assets, Net - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2015
Business Acquisition [Line Items]
Weighted-average remaining amortization period of intangible assets		10 years 7 months 6 days
Core Nano Carrier Technology [Member]
Business Acquisition [Line Items]
Amortization period of intangible assets		10 years
Other In-process Research and Development Program [Member]
Business Acquisition [Line Items]
Impairment charge	$ 0.8
Hermes BioSciences, Inc. [Member]
Business Acquisition [Line Items]
Acquired IPR&D recognized in a business combination		$ 7.0
Acquisition date		Oct. 06, 2009
Hermes BioSciences, Inc. [Member] \| Core Nano Carrier Technology [Member]
Business Acquisition [Line Items]
Acquired intangible assets		$ 3.2
Hermes BioSciences, Inc. [Member] \| Antibody Targeted Nanotherapeutic Program with Chemotherapy Drug [Member]
Business Acquisition [Line Items]
Acquired IPR&D recognized in a business combination		2.8
Hermes BioSciences, Inc. [Member] \| Nanotherapeutic Program with Chemotherapy Drug [Member]
Business Acquisition [Line Items]
Acquired IPR&D recognized in a business combination		3.4
Hermes BioSciences, Inc. [Member] \| Other In-process Research and Development Program [Member]
Business Acquisition [Line Items]
Acquired IPR&D recognized in a business combination		$ 0.8

Goodwill and Intangible Assets, Net - Schedule of Changes in the Carrying Value of Goodwill, IPR&D and Intangible Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Intangible Assets By Major Class [Line Items]
Intangible asset	$ 7,355	$ 7,725
Goodwill	3,605	3,605	$ 3,605
Core Nano Carrier Technology [Member]
Intangible Assets By Major Class [Line Items]
Intangible asset	1,205	1,525	1,845
Amortization	(320)	(320)
ONIVYDE [Member]
Intangible Assets By Major Class [Line Items]
Intangible asset	3,350
Amortization	(50)
Reclassification of IPR&D to definite-lived intangible assets	3,400
IPR&D Program [Member]
Intangible Assets By Major Class [Line Items]
IPR&D	2,800	$ 6,200	$ 6,200
Reclassification of IPR&D to definite-lived intangible assets	$ (3,400)

Goodwill and Intangible Assets, Net - Schedule of Expected Amortization Expense for Intangible Assets for the Next Five-Year Period (Detail) $ in Thousands	Dec. 31, 2015 USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2016	$ 578
2017	578
2018	578
2019	503
2020	$ 258

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 51,226	$ 38,642
Less: Accumulated depreciation	(29,311)	(24,140)
Total property and equipment, net	21,915	14,502
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	19,305	16,214
IT Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	7,742	3,113
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	21,026	18,219
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	910	624
Construction in Process [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 2,243	$ 472

Property and Equipment, Net - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property Plant and Equipment Useful Life and Values [Abstract]
Depreciation expense	$ 5,500,000	$ 4,200,000	$ 2,800,000
Gross amount of fully depreciated fixed assets disposed	303,000	1,603,000	210,000
Recognized impairment charges	$ 0	$ 0	$ 0

Accounts Payable, Accrued Expenses and Other - Schedule of Accounts Payable, Accrued Expenses and Other (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Payables and Accruals [Abstract]
Accounts payable	$ 5,049	$ 2,510
Accrued goods and services	14,295	17,481
Accrued clinical trial costs	12,764	7,637
Accrued drug purchase costs	7,460
Accrued payroll and related benefits	9,009	6,166
Accrued interest	3,041	2,956
Accrued dividends payable	19	19
Deferred tax incentives	445	467
Total accounts payable, accrued expenses and other	$ 52,082	$ 37,236

Borrowings - 2022 Notes - Additional Information (Detail) - USD ($)		12 Months Ended
	Dec. 22, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Debt Instruments [Line Items]
Debt issuance costs			$ 100,000
Debt maturity date		Jul. 15, 2020
Interest expense		$ 19,232,000	18,230,000	$ 10,938,000
Change of Control Event [Member]
Schedule Of Debt Instruments [Line Items]
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest	101.00%
Asset Sale Event [Member]
Schedule Of Debt Instruments [Line Items]
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest	100.00%
Hercules [Member]
Schedule Of Debt Instruments [Line Items]
Interest expense		$ 5,400,000	$ 4,700,000	$ 4,900,000
2022 Notes [Member]
Schedule Of Debt Instruments [Line Items]
Aggregate principal amount of loan	$ 175,000,000
Net proceeds from the debt issuance	$ 168,500,000
Interest rate (as a percent)	11.50%
Debt issuance costs	$ 900,000
Semi-annual installments of principal	$ 21,875,000
Debt maturity date	Dec. 15, 2022
Effective interest rate		12.32%
Interest expense		$ 500,000
2022 Notes [Member] \| Conversion Terms, Fundamental Changes [Member]
Schedule Of Debt Instruments [Line Items]
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest		100.00%
2022 Notes [Member] \| Hercules [Member]
Schedule Of Debt Instruments [Line Items]
Aggregate principal amount of loan		$ 40,000,000

Borrowings - Convertible Notes - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended	12 Months Ended
	Jul. 31, 2013	Jul. 31, 2013	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Debt Instruments [Line Items]
Debt maturity date				Jul. 15, 2020
Interest expense				$ 19,232,000	$ 18,230,000	$ 10,938,000
Convertible Notes [Member]
Schedule Of Debt Instruments [Line Items]
Gross proceeds from the debt issuance		$ 125,000,000
Net proceeds from the debt issuance		$ 120,600,000
Interest rate (as a percent)	4.50%	4.50%	4.50%	4.50%
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be convertible	30 days		30 days
Convertibility of debt, closing price of stock test, percentage of stock price to conversion price for the notes that must be exceeded	130.00%		130.00%
Number of consecutive business days immediately after any five consecutive trading day period during the note measurement period	5 days
Number of consecutive trading days before five consecutive business days during the note measurement period	5 days
Conversion ratio, principal amount	$ 1,000	$ 1,000
Conversion rate of common stock shares per $1,000 principal amount	160
Initial conversion price of shares (in dollars per share)	$ 6.25	$ 6.25
Minimum percentage of aggregate principal amount held by bondholders to declare notes due and payable	25.00%
Percentage of principal amount due and payable upon event of default	100.00%
Effective interest rate used to compute initial fair value (as a percent)	15.00%
Fair value of indebtedness	$ 71,200,000	$ 71,200,000
Embedded conversion option	53,800,000	53,800,000
Underwriting discounts and commissions and offering expenses	4,400,000
Debt issuance costs allocated to unamortized debt discount	2,500,000	2,500,000
Debt issuance costs attributable to embedded conversion option	$ 1,900,000	$ 1,900,000
Interest expense				$ 13,700,000	$ 13,700,000	$ 6,200,000
Convertible Notes [Member] \| Conversion Terms, Fundamental Changes [Member]
Schedule Of Debt Instruments [Line Items]
Redemption price as percentage of principal amount of notes plus accrued and unpaid interest	100.00%
Convertible Notes [Member] \| Conversion Terms, Event of Default [Member]
Schedule Of Debt Instruments [Line Items]
Percentage of principal amount due and payable upon event of default arising out of certain bankruptcy events	100.00%
Convertible Notes [Member] \| Minimum [Member]
Schedule Of Debt Instruments [Line Items]
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be convertible	20 days		20 days
Convertible Notes [Member] \| Maximum [Member]
Schedule Of Debt Instruments [Line Items]
Convertibility of debt, trading price of debt test, percentage of closing price of stock used in calculation	98.00%

Borrowings - Loan Agreement - Additional Information (Detail) - USD ($) $ in Thousands				3 Months Ended	12 Months Ended
	Dec. 22, 2015	Feb. 25, 2015	Nov. 06, 2014	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Nov. 30, 2012
Schedule Of Debt Instruments [Line Items]
Extension period for interest-only payment			4 months
Repayment of notes				$ 40,000
Debt issuance costs						$ 100
Interest expense					$ 19,232	18,230	$ 10,938
Loan and Security Agreement [Member]
Schedule Of Debt Instruments [Line Items]
Discount on loan recorded as a non-current liability to be paid upon full repayment or maturity of the loans				1,200	1,200
2022 Notes [Member]
Schedule Of Debt Instruments [Line Items]
Aggregate principal amount of loan	$ 175,000
Debt issuance costs				5,840	5,840
Debt issuance costs	$ 900
Interest expense					500
2022 Notes [Member] \| Modified Loan Agreement [Member]
Schedule Of Debt Instruments [Line Items]
Debt issuance costs				300	300
Hercules [Member]
Schedule Of Debt Instruments [Line Items]
Initial debt discount				1,600	1,600
Interest expense					5,400	$ 4,700	$ 4,900
Hercules [Member] \| Loan and Security Agreement [Member]
Schedule Of Debt Instruments [Line Items]
Aggregate principal amount of loan		$ 40,000						$ 40,000
Outstanding principal balance repayment start date		Jun. 01, 2016
Outstanding principal balance repayment end date		Nov. 01, 2018
Extended maturity period on principal payment		6 months
Hercules [Member] \| 2022 Notes [Member]
Schedule Of Debt Instruments [Line Items]
Aggregate principal amount of loan				$ 40,000	40,000
Hercules [Member] \| 2022 Notes [Member] \| Modified Loan Agreement [Member]
Schedule Of Debt Instruments [Line Items]
Debt issuance costs					$ 900

Borrowings - Convertible Notes - Silver Creek - Additional Information (Detail) - Silver Creek [Member] - USD ($)	1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015
Schedule Of Debt Instruments [Line Items]
Ownership interest (as a percent)	74.00%	60.00%	64.00%
Non-controlling interest		$ 400,000	$ 800,000
Silver Creek Convertible Note [Member]
Schedule Of Debt Instruments [Line Items]
Gross proceeds from the debt issuance	$ 1,600,000	$ 1,000,000	$ 900,000
Interest rate (as a percent)				6.00%
Discount on automatic conversion into the next qualifying equity financing (as a percent)	25.00%
Derivative liability	$ 200,000
Silver Creek Convertible Note [Member] \| Minimum [Member]
Schedule Of Debt Instruments [Line Items]
Amount of gross proceeds from qualifying equity financing in which holders would automatically convert into the next qualifying equity financing at a 25% discount	$ 4,000,000

Borrowings - Schedule of Future Minimum Payments under the Loans Payable (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Less current portion		$ (13,315)
Long-term debt, net of current portion	$ 257,655	$ 106,687
Convertible Notes [Member]
Debt Instrument [Line Items]
2016	5,625
2017	5,625
2018	5,625
2019	5,625
2020 and thereafter	130,625
Loans payable, gross including contractual interest	153,125
Less interest	(28,125)
Less unamortized discount	(36,505)
Less current portion	0
Long-term debt, net of current portion	88,495
2022 Notes [Member]
Debt Instrument [Line Items]
2016	19,734
2017	20,125
2018	20,125
2019	62,617
2020 and thereafter	157,664
Loans payable, gross including contractual interest	280,265
Less interest	(105,265)
Less unamortized discount	(5,840)
Less current portion	0
Long-term debt, net of current portion	$ 169,160

Inventory - Schedule of Inventory (Detail) $ in Thousands	Dec. 31, 2015 USD ($)
Inventory Disclosure [Abstract]
Raw materials	$ 900
Work in process	2,743
Finished goods	74
Total inventory	$ 3,717

Stock Warrants - Schedule of Common Stock Warrant Activity of the Company (Detail) - Common Stock Warrant [Member] - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Warrant or Right [Line Items]
Beginning Balance	2,381	2,777	2,842
Exercised (in shares)	(2,355)	(396)	(65)
Cancelled (in shares)	(26)
Ending Balance		2,381	2,777
Beginning Balance	$ 3.00	$ 3.05	$ 3.05
Exercised (per share)	3.00	3.38	2.82
Cancelled (per share)	$ 3.00
Ending Balance		$ 3.00	$ 3.05

Common Stock - Additional Information (Detail) - USD ($)		1 Months Ended	3 Months Ended
	Jul. 13, 2015	Jul. 31, 2013	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Class of Stock [Line Items]
Shares of common stock sold in underwritten public offering		5,800,000
Public offering price		$ 5.00
Net proceeds from issuance of common stock after deducting commissions and offering expenses		$ 26,700,000
Common stock, shares issued				115,871,000	106,697,000
Common stock, shares authorized				200,000,000	200,000,000
Common stock, par value				$ 0.01	$ 0.01
Common stock, shares outstanding				115,871,000	106,697,000
Cowen and Company Llc [Member] \| At the Market Offering [Member]
Class of Stock [Line Items]
Net proceeds from issuance of common stock after deducting commissions and offering expenses			$ 38,600,000
Common stock, shares issued			3,800,000
Maximum [Member] \| Cowen and Company Llc [Member] \| At the Market Offering [Member]
Class of Stock [Line Items]
Aggregate sales price of offering	$ 40,000,000

Common Stock - Schedule of Shares Reserved for Future Issuance (Detail) - shares shares in Thousands	Dec. 31, 2015	Dec. 31, 2014
Common Stock Warrants [Member]
Class of Stock [Line Items]
Shares reserved for future issuance		2,381
Outstanding Options To Purchase Common Stock [Member]
Class of Stock [Line Items]
Shares reserved for future issuance	19,211	19,567
Stock Incentive Plan 2011 [Member]
Class of Stock [Line Items]
Shares reserved for future issuance	2,462	1,983
Conversion of the Convertible Notes [Member]
Class of Stock [Line Items]
Shares reserved for future issuance	25,000	25,000

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended			12 Months Ended			21 Months Ended
	Feb. 28, 2015	Mar. 31, 2014	Feb. 28, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted				3,720,000
Weighted-average grant date fair value of stock options				$ 5.80	$ 3.41	$ 3.59
Aggregate intrinsic value of options exercised				$ 30.9	$ 19.8	$ 2.7
Unrecognized compensation cost related to nonvested stock awards				$ 18.3
Weighted average period over which unrecognized compensation cost is expected to be recognized				1 year 9 months 18 days
Stock Incentive Plan 2011 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional common stock available for issuance (in shares)	3,700,000	3,600,000	3,400,000
Shares of common stock available for grant (in shares)				2,500,000
Number of Shares, Granted				3,700,000	3,900,000	3,300,000
Stock Incentive Plan 2011 [Member] \| Non Employee [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Granted				0	0	100,000
Stock Incentive Plan 2011 [Member] \| Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options vesting period							1 year
Stock Incentive Plan 2011 [Member] \| Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options vesting period				3 years

Stock-Based Compensation - Schedule of Recognized Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense for employee awards	$ 15,293	$ 12,929	$ 10,762
Stock-based compensation expense for non-employee awards	58	268	(29)
Total stock-based compensation	15,351	13,197	10,733
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense for employee awards	8,271	6,864	5,954
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense for employee awards	$ 7,022	$ 6,065	$ 4,808

Stock-Based Compensation - Schedule of Assumptions Used to Calculate Fair Value of Options Granted to Employees (Detail) - Options to Purchase Common Stock [Member]	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected dividend yield	0.00%	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.50%	1.60%	0.10%
Expected term	5 years	5 years	5 years 3 months 18 days
Expected volatility	66.00%	64.00%	67.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.80%	2.00%	1.90%
Expected term	5 years 10 months 24 days	5 years 10 months 24 days	5 years 10 months 24 days
Expected volatility	67.00%	72.00%	70.00%

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Shares, Outstanding, Beginning balance	19,556
Number of Shares, Granted	3,720
Number of Shares, Exercised	(3,606)
Number of Shares, Forfeited	(459)
Number of Shares, Outstanding, Ending balance	19,211	19,556
Number of shares vested and expected to vest	18,923
Number of stock option exercisable	14,783
Weighted Average Exercise Price, Outstanding, Beginning balance	$ 4.47
Weighted Average Exercise Price, Granted	9.63
Weighted Average Exercise Price, Exercised	2.75
Weighted Average Exercise Price, Forfeited	7.36
Weighted Average Exercise Price, Outstanding, Ending balance	5.72	$ 4.47
Weighted average exercise price of shares vested and expected to vest (in dollars per share)	5.68
Weighted average exercise price for exercisable option (in dollars per share)	$ 5.01
Weighted Average Remaining Contractual Term	6 years 2 months 27 days	6 years 2 months 1 day
Weighted Average Remaining Contractual Term, Vested and expected to vest	6 years 2 months 12 days
Weighted Average Remaining Contractual Term, Exercisable	5 years 5 months 23 days
Aggregate Intrinsic Value, Outstanding	$ 47,963	$ 133,599
Aggregate Intrinsic Value, Vested and expected to vest	47,818
Aggregate Intrinsic Value, Exercisable	$ 44,173

Income Taxes - Schedule of Reconciliation of the Company's Effective Tax Rate to the Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Federal income tax at statutory federal rate	35.00%	35.00%	35.00%
State taxes	1.00%	3.10%	4.30%
Permanent differences	(6.40%)	(9.10%)	(2.00%)
Stock-based compensation	(1.30%)	(1.70%)	(0.60%)
Tax credits	21.30%	30.50%	12.40%
Foreign rate differential		(2.30%)	(2.80%)
Change in deferred state tax rate	(2.30%)
Other	(0.50%)	4.50%	(1.50%)
Change in valuation allowance	(46.80%)	(60.00%)	(44.80%)
Effective income tax rate	0.00%	0.00%	0.00%

Income Taxes - Schedule of Temporary Differences That Give Rise to Significant Net Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred tax assets
Net operating losses	$ 182,992	$ 160,333
Capitalized research and development expenses	21,444	30,929
Credit carryforwards	93,113	62,362
Depreciation	2,128	2,579
Deferred compensation	11,664	10,682
Accrued expenses	1,807	12
Deferred revenue	10,999	960
Other temporary differences	17,235	9,195
Total gross deferred tax asset	341,382	277,052
Valuation allowance	(326,577)	(257,489)	$ (207,304)	$ (169,651)
Net deferred tax asset	14,805	19,563
Deferred tax liabilities
Intangible assets	(2,667)	(3,106)
Debt discount	(12,138)	(16,457)
Net deferred taxes	$ 0	$ 0

Income Taxes - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Operating Loss Carryforwards [Line Items]
Federal and state net operating loss carryforwards relate to deductions for stock option compensation	$ 36.5
Federal Orphan Drug Credits	62.7
Federal [Member]
Operating Loss Carryforwards [Line Items]
NOL	509.8
Federal [Member] \| Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	23.7
State [Member]
Operating Loss Carryforwards [Line Items]
NOL	356.9
Federal and state net operating loss carryforwards relate to deductions for stock option compensation	24.7
State [Member] \| Research and Development [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	9.6
State [Member] \| Investment [Member]
Operating Loss Carryforwards [Line Items]
Amount of tax credit carryforward	$ 0.8

Income Taxes - Schedule of Changes in the Valuation Allowance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Balance at beginning of period	$ 257,489	$ 207,304	$ 169,651
Additions	69,088	50,185	37,653
Deductions	0	0	0
Balance at end of period	$ 326,577	$ 257,489	$ 207,304

Commitments and Contingencies - Additional Information (Detail) $ in Millions		1 Months Ended	12 Months Ended
	Feb. 23, 2015 USD ($) ft²	Aug. 31, 2012 USD ($) ft²	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Operating Leased Assets [Line Items]
Total rent expense			$ 7.4	$ 5.9	$ 5.5
Aggregate space that the entity will occupy under the amended lease agreement \| ft²		109,000
Aggregate leasehold improvement allowance	$ 1.3
July 22, 2015 Amendment [Member]
Operating Leased Assets [Line Items]
Leased space \| ft²	45,463
Additional lease payments due total	$ 9.3
Aggregate landlord reimbursable tenant improvements outstanding under the existing lease and the lease amendment			$ 8.2	$ 8.2
Maximum [Member]
Operating Leased Assets [Line Items]
Additional reimbursement for tenant improvements agreed by landlord per lease amendment		$ 8.2

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Under Non-cancelable Operating Leases (Detail) - July 22, 2015 Amendment [Member] $ in Thousands	Dec. 31, 2015 USD ($)
Loss Contingencies [Line Items]
2016	$ 7,543
2017	7,690
2018	7,846
2019	$ 3,953

Related Party Transactions - Additional Information (Detail) - Silver Creek [Member]	Dec. 31, 2015	Dec. 31, 2014
Series A Preferred Stock [Member]
Related Party Transaction [Line Items]
Shares owned by employees and directors of the parent company (as a percent)		6.00%
Series A and B Preferred Stock [Member]
Related Party Transaction [Line Items]
Shares owned by employees and directors of the parent company (as a percent)	7.00%

Selected Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Product revenues, net	$ 4,328								$ 4,328	$ 0	$ 0
License and collaboration revenues	17,090	$ 16,440	$ 36,558	$ 14,842	$ 33,905	$ 28,002	$ 27,815	$ 13,034	84,930	102,756	47,786
Cost of product revenues	46								46	0	0
Research and development expenses	44,740	37,763	42,806	35,679	30,744	43,632	33,795	30,324	160,988	138,495	147,139
Selling, general and administrative expenses	19,335	16,956	12,315	9,189	8,277	8,095	7,921	6,224	57,795	30,517	21,187
Net loss	(48,068)	(42,386)	(22,901)	(34,432)	(9,477)	(28,038)	(18,290)	(27,754)	(147,787)	(83,559)	(130,685)
Net loss attributable to Merrimack Pharmaceuticals, Inc.	$ (47,826)	$ (42,594)	$ (22,778)	$ (34,759)	$ (9,696)	$ (27,901)	$ (18,109)	$ (27,585)	$ (147,957)	$ (83,291)	$ (130,925)
Net loss per share available to common stockholders-basic and diluted	$ (0.41)	$ (0.38)	$ (0.21)	$ (0.32)	$ (0.09)	$ (0.27)	$ (0.17)	$ (0.27)	$ (1.33)	$ (0.80)	$ (1.32)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Retirement Plan	12 Months Ended
Retirement Plan	Dec. 31, 2015
Postemployment Benefits [Abstract]
Retirement Plan	19. Retirement Plan On May 31, 2002, the Company established a 401(k) defined contribution savings plan (the “401(k) Plan”) for its employees who meet certain service period and age requirements. Contributions are permitted up to the maximum allowed under the Internal Revenue Code of each covered employee’s salary. The 401(k) Plan permits the Company to contribute at its discretion. For the years ended December 31, 2015, 2014 and 2013, the Company made contributions of $1.1 million, $0.8 million and $0.7 million, respectively, to the 401(k) Plan.

Stock Warrants - Additional Information (Detail) - Common Stock Warrant [Member] - shares	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Class of Warrant or Right [Line Items]
Number of warrants cashless exercised	2,295,000	75,000	65,000
Number of common stock issued as a result of cashless exercise of warrants	1,695,000	38,000	35,000