Merrimack Pharmaceuticals (MACK) 10-Q 8 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	May 03, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Trading Symbol	MACK
Entity Registrant Name	MERRIMACK PHARMACEUTICALS INC
Entity Central Index Key	1,274,792
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		13,342,784

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 34,268	$ 93,441
Marketable securities	41,998
Prepaid expenses and other current assets	844	1,605
Total current assets	77,110	95,046
Restricted cash	674	674
Property and equipment, net	5,358	6,467
Equity method investment	9,805	10,551
Other assets	4,548	4,588
Total assets	97,495	117,326
Current liabilities:
Accounts payable, accrued expenses and other	15,323	17,606
Deferred rent	2,211	2,171
Total current liabilities	17,534	19,777
Deferred rent, net of current portion	651	1,209
Other long-term liabilities	56	56
Total liabilities	18,241	21,042
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.01 par value: 10,000 shares authorized at March 31, 2018 and December 31, 2017; no shares issued or outstanding at March 31, 2018 or December 31, 2017
Common stock, $0.01 par value: 20,000 shares authorized at March 31, 2018 and December 31, 2017; 13,343 shares issued and outstanding at March 31, 2018 and December 31, 2017	1,334	1,334
Additional paid-in capital	578,485	577,721
Accumulated deficit	(500,553)	(482,771)
Accumulated other comprehensive loss	(12)
Total stockholders’ equity	79,254	96,284
Total liabilities and stockholders’ equity	$ 97,495	$ 117,326

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017
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	20,000,000	20,000,000
Common stock, shares issued	13,343,000	13,343,000
Common stock, shares outstanding	13,343,000	13,343,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating expenses:
Research and development expenses	$ 13,106,000	$ 21,605,000
General and administrative expenses	4,270,000	5,634,000
Total operating expenses	17,376,000	27,239,000
Loss from continuing operations	(17,376,000)	(27,239,000)
Other income and expenses:
Interest income	275,000	14,000
Interest expense		(1,979,000)
Other income (expense), net	(681,000)	(2,000)
Total other income and expenses	(406,000)	(1,967,000)
Net loss from continuing operations	(17,782,000)	(29,206,000)
Discontinued operations:
Loss from discontinued operations, net of tax	0	(947,000)
Net loss	(17,782,000)	(30,153,000)
Net loss attributable to non-controlling interest		(467,000)
Net loss attributable to Merrimack Pharmaceuticals, Inc.	(17,782,000)	(29,686,000)
Other comprehensive loss:
Unrealized loss on marketable securities	(12,000)
Other comprehensive loss	(12,000)
Comprehensive loss	(17,794,000)	(29,686,000)
Amounts attributable to Merrimack Pharmaceuticals, Inc.:
Net loss from continuing operations	(17,782,000)	(28,739,000)
Loss from discontinued operations, net of tax		(947,000)
Net loss attributable to Merrimack Pharmaceuticals, Inc.	$ (17,782,000)	$ (29,686,000)
Basic and dilutive net loss per common share
Net loss from continuing operations	$ (1.33)	$ (2.20)
Net loss from discontinued operations, net of tax		(0.07)
Net loss per share	$ (1.33)	$ (2.27)
Weighted-average common shares used per share calculations—basic and diluted	13,343	13,059

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Cash Flows - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities
Net loss	$ (17,782,000)	$ (30,153,000)
Loss from discontinued operations, net of tax	0	(947,000)
Loss from continuing operations	(17,782,000)	(29,206,000)
Adjustments to reconcile net loss to net cash used in operating activities
Non-cash interest expense		1,508,000
Depreciation and amortization expense	1,239,000	1,182,000
Premiums paid on marketable securities	(51,000)
Amortization and accretion on marketable securities	(141,000)
Stock-based compensation expense	764,000	796,000
Loss on equity method investment	746,000
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	801,000	(372,000)
Accounts payable, accrued expenses and other	(2,397,000)	8,054,000
Deferred rent	(518,000)	(86,000)
Net cash used in continuing operations for operating activities	(17,339,000)	(18,124,000)
Net cash provided by discontinuing operations for operating activities		7,968,000
Net cash used in operating activities	(17,339,000)	(10,156,000)
Cash flows from investing activities
Purchase of property and equipment	(16,000)	(290,000)
Purchases of marketable securities	(41,818,000)
Net cash used in investing activities	(41,834,000)	(290,000)
Cash flows from financing activities
Proceeds from exercise of options to purchase common stock		4,053,000
Net cash provided by financing activities		6,077,000
Net decrease in cash, cash equivalents and restricted cash	(59,173,000)	(4,369,000)
Cash, cash equivalents and restricted cash, beginning of period	94,217,000	22,300,000
Cash, cash equivalents and restricted cash, end of period	35,044,000	17,931,000
Non-cash investing and financing activities
Purchases of property and equipment in accounts payable, accrued expenses and other	$ 114,000	34,000
Receivables related to property and equipment sale in other current assets		76,000
Supplemental disclosure of cash flows
Cash paid for interest		1,368,000
Silver Creek Pharmaceuticals Inc [Member]
Cash flows from financing activities
Proceeds from issuance of Series C preferred stock by Silver Creek Pharmaceuticals, Inc., net of issuance costs		$ 2,024,000

Nature of the Business

Nature of the Business	3 Months Ended
	Mar. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business Merrimack Pharmaceuticals, Inc. (the “Company”) is a clinical stage biopharmaceutical company based in Cambridge, Massachusetts that is outthinking cancer by targeting biomarker-defined cancers. The Company’s vision is to ensure that cancer patients and their families live fulfilling lives. The Company’s mission is to transform cancer care through the smart design and development of targeted solutions based on a deep understanding of cancer pathways and biological markers. All of the Company’s development programs, including four clinical trials and six candidates in preclinical development, fit into the Company’s strategy of (1) understanding the biological problems it is trying to solve, (2) designing specific solutions against the problems it is trying to solve and (3) developing those solutions for biomarker-selected patients. This three-pronged strategy seeks to ensure optimal patient outcomes. The Company owns worldwide development and commercial rights to all of its clinical and preclinical programs. The Company’s most advanced assets and a description of the status of each asset are as follows: • MM-121 (seribantumab) : MM-121 is a fully human monoclonal antibody that binds to the ErbB3 (HER3) receptor and targets heregulin positive cancers. There are two active development programs for MM-121, each in a Phase 2 clinical trial. The Company is conducting the global, open-label, biomarker-selected, Phase 2 randomized SHERLOC clinical trial evaluating MM-121 in combination with docetaxel in patients with heregulin positive non-small cell lung cancer. The Company is also conducting the global, double-blinded, placebo-controlled, biomarker-selected, Phase 2 randomized SHERBOC clinical trial evaluating MM-121 in combination with fulvestrant in patients with heregulin positive, hormone receptor positive, ErbB2 (HER2) negative, metastatic breast cancer; • MM-141 (istiratumab) : MM-141 is a fully human tetravalent bispecific antibody designed to block tumor survival signals by targeting receptor complexes containing the insulin-like growth factor 1 (“IGF-1”), receptor and ErbB3 (HER3) cell surface receptor. The Company is conducting and has completed enrollment of the global, double-blinded, placebo-controlled, Phase 2 randomized CARRIE clinical trial evaluating MM-141 in combination with nab-paclitaxel and gemcitabine in patients with previously untreated metastatic pancreatic cancer with high serum levels of free IGF-1; and • MM-310 : MM-310 is an antibody-directed nanotherapeutic that targets the ephrin receptor A2 (“EphA2”) receptor and contains a novel prodrug of the highly potent chemotherapy docetaxel. The EphA2 receptor is highly expressed in most solid tumor types, such as prostate, ovarian, bladder, gastric, pancreatic and lung cancers. The Company is conducting a Phase 1 clinical trial to evaluate safety and preliminary activity of MM-310 in patients with solid tumors and to identify the maximum tolerated dose. 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 capital, adequate personnel, infrastructure and extensive compliance reporting capabilities. The Company’s product candidates are in development, and none are approved for any indication by the U.S. Food and Drug Administration (“FDA”) or any other regulatory agency. There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained or maintained, that any products developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies, among others. In addition, the Company is dependent upon the services of its employees and consultants. In accordance with Accounting Standards Codification (“ASC”) 205-40, Going Concern The Company will ultimately need to seek additional funding through equity offerings, debt financings, collaborations, licensing arrangements and other marketing and distribution arrangements, partnerships, joint ventures, combinations or divestitures of one or more of its businesses. 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 collaborative arrangements or divest its assets. 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 Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying condensed consolidated financial statements reflect the operations of Merrimack Pharmaceuticals, Inc. and its wholly owned subsidiary. All intercompany accounts and transactions have been eliminated. The condensed consolidated financial statements are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accounting policies followed in the preparation of the interim condensed consolidated financial statements are consistent in all material respects with those presented in Note 1 to the financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017. Certain reclassifications have been made to the prior year’s condensed consolidated balance sheet and condensed consolidated statement of cash flows to enhance comparability with the current year’s condensed consolidated financial statements presentation. These reclassifications had no effect on previously reported net income within the condensed consolidated statement of operations and comprehensive loss. Consolidation The accompanying condensed consolidated financial statements reflect Merrimack Pharmaceuticals, Inc. and its wholly owned subsidiary. For the three months ended March 31, 2017, the condensed consolidated financial statements also include the accounts of Silver Creek Pharmaceuticals, Inc. (“Silver Creek”). For the three months ended March 31, 2017, Silver Creek represented a variable interest entity that the Company consolidated as the primary beneficiary. In the third quarter of 2017, the Company deconsolidated Silver Creek from its financial statements since the Company was no longer the primary beneficiary of Silver Creek. The Company’s ownership percentage decreased to less than 50% and the Company no longer controlled Silver Creek’s board of directors or directed the activities that had the most significant impact on Silver Creek’s economic performance. The Company accounts for its investment in Silver Creek under the equity method of accounting. On April 3, 2017, the Company completed the sale of its right, title and interest in the non-cash assets, equipment, inventory, contracts and intellectual property primarily related to developing, manufacturing and commercializing ONIVYDE and MM-436 (the “Commercial Business”). As of March 31, 2017, the Commercial Business met all the conditions to be classified as a discontinued operation since the disposal of the Commercial Business represented a strategic shift that had a major effect on the Company’s operations and financial results. Therefore, the operating results of the Commercial Business are reported as a loss from discontinued operations, net of tax in the condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2017. During the three months ended March 31, 2018, there were no discontinued operations. Unaudited Interim Financial Information The condensed consolidated balance sheet as of December 31, 2017 was derived from audited financial statements, but does not include all disclosures required by GAAP. The condensed consolidated balance sheet as of March 31, 2018, the condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2018 and 2017 and the condensed consolidated statements of cash flows for the three months ended March 31, 2018 and 2017 are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of March 31, 2018, the results of its operations for the three months ended March 31, 2018 and 2017, and its statements of cash flows for the three months ended March 31, 2018 and 2017. The financial data and other information disclosed in the notes related to the three months ended March 31, 2018 and 2017 are unaudited. The results for the three months ended March 31, 2018 and 2017 are not necessarily indicative of results to be expected for the year ending December 31, 2018, any other interim periods, or any future year or period. The unaudited interim financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements and the notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 filed with the SEC on March 12, 2018. Condensed Consolidated Statements of Cash Flows The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the statement of financial position that sum to the total of the same such amounts shown in the statement of cash flows: (in thousands) March 31, 2018 March 31, 2017 Cash and cash equivalents $ 34,268 $ 17,155 Restricted cash in prepaid expenses and other current assets 102 — Restricted cash (short term) — 102 Restricted cash (long term) 674 674 Total cash, cash equivalents and restricted cash shown in the condensed consolidated statement of cash flows $ 35,044 $ 17,931 Restricted cash included in prepaid expenses and other current assets and restricted cash long term on the statement of financial position represent amounts pledged as collateral for operating lease obligations as contractually required. This restriction will lapse when the arrangements expire. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates, assumptions and judgments that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates, assumptions and judgments reflected in these condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates. Marketable Securities Marketable securities consist of investments with original maturities greater than ninety days. The Company has classified its investments with maturities beyond one year as short term based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. The Company considers its investment portfolio of marketable debt securities as available-for-sale. Accordingly, these marketable debt securities are recorded at fair value and unrealized gains and losses are reported as a component of accumulated other comprehensive loss in stockholders’ equity. Realized gains and losses and declines in value judged to be other than temporary are included as a component of other income (expense), net based on the specific identification method. When determining whether a decline in value is other than temporary, the Company considers various factors, including whether the Company has the intent to sell the security, and whether it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	3. Fair Value of Financial Instruments 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. The following tables show assets measured at fair value on a recurring basis as of March 31, 2018 and December 31, 2017: March 31, 2018 (in thousands) Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 6,785 $ — $ — Corporate debt securities — 2,009 — Commercial paper — 13,781 — Totals $ 6,785 $ 15,790 $ — Marketable securities: Corporate debt securities $ — $ 6,217 $ — Commercial paper — 21,841 — Government securities — 13,940 — Totals $ — $ 41,998 $ — December 31, 2017 (in thousands) Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 89,310 $ — $ — Totals $ 89,310 $ — $ — During the three months ended March 31, 2018 and the year ended December 31, 2017, there were no transfers between Level 1 and Level 2. The fair value of Level 2 instruments classified as cash equivalents and marketable debt securities were determined through third-party pricing services. The carrying amounts reflected in the condensed consolidated balance sheets for accounts payable, accrued expenses and other liabilities approximate fair value due to their short-term maturities.

Marketable Securities and Cash

Marketable Securities and Cash Equivalents	3 Months Ended
	Mar. 31, 2018
Investments Debt And Equity Securities [Abstract]
Marketable Securities and Cash Equivalents	4. Marketable Securities and Cash Equivalents The following table summarizes the Company’s marketable securities and cash equivalents as of March 31, 2018. The Company did not hold any marketable securities as of December 31, 2017. March 31, 2018 (in thousands) Amortized Cost Unrealized Losses Fair Value Cash equivalents: Money market funds $ 6,785 $ — $ 6,785 Corporate debt securities 2,010 (1 ) 2,009 Commercial paper 13,781 — 13,781 Total cash equivalents $ 22,576 $ (1 ) $ 22,575 Marketable securities: Corporate debt securities $ 6,227 $ (10 ) $ 6,217 Commercial paper 21,841 — 21,841 Government securities 13,941 (1 ) 13,940 Total marketable securities $ 42,009 $ (11 ) $ 41,998 Total cash equivalents and marketable securities $ 64,585 $ (12 ) $ 64,573

Accounts Payable, Accrued Expen

Accounts Payable, Accrued Expenses and Other	3 Months Ended
	Mar. 31, 2018
Payables And Accruals [Abstract]
Accounts Payable, Accrued Expenses and Other	5. Accounts Payable, Accrued Expenses and Other Accounts payable, accrued expenses and other as of March 31, 2018 and December 31, 2017 consisted of the following: (in thousands) March 31, 2018 December 31, 2017 Accounts payable $ 2,560 $ 2,887 Accrued goods and services 4,027 5,682 Accrued clinical trial costs 4,925 3,901 Accrued drug purchase costs 918 222 Accrued payroll and related benefits 1,240 2,884 Accrued restructuring expenses 251 628 Deferred tax incentives 1,402 1,402 Total accounts payable, accrued expenses and other $ 15,323 $ 17,606

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	6. Stock-Based Compensation The Company’s 2011 Stock Incentive Plan (the “2011 Plan”) is administered by the Company’s Board of Directors 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. At March 31, 2018, there were 0.5 million shares remaining available for grant under the 2011 Plan. During the three months ended March 31, 2018 and 2017, the Company issued options to purchase 0.6 million and 0.0 million shares of common stock, respectively. These options generally vest over a three-year period for employees. Options granted to directors generally vest immediately. The fair value of stock options granted to employees during the three months ended March 31, 2018 and 2017 was estimated at the date of grant using the following assumptions: Three Months Ended March 31, 2018 2017 Risk-free interest rate 2.3 – 2.7% 2.1 % Expected dividend yield 0% 0% Expected term 5.8 years 5.8 years Expected volatility 62 – 63% 67 – 68% 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 Company recognized stock-based compensation expense during the three months ended March 31, 2018 and 2017 as follows: Three Months Ended March 31, (in thousands) 2018 2017 Employee awards: Research and development expense $ 334 $ 468 General and administrative expense 430 328 Total stock-based compensation expense $ 764 $ 796 The following table summarizes stock option activity during the three months ended March 31, 2018: Weighted-Average Remaining Aggregate (in thousands, except per share amounts) Options Weighted-Average Exercise Price Contractual Term (in years) Intrinsic Value Outstanding at December 31, 2017 1,616 $ 22.07 6.65 $ 60,031 Granted 566 $ 10.74 Exercised — $ — Forfeited (145 ) $ 21.04 Outstanding at March 31, 2018 2,037 $ 19.00 7.22 $ — Vested and expected to vest at March 31, 2018 2,036 $ 19.00 7.22 $ — Exercisable at March 31, 2018 1,032 $ 25.17 4.97 $ — The weighted-average grant date fair value per share of stock options granted during the three months ended March 31, 2018 and 2017 was $6.26 and $24.30, respectively. The aggregate intrinsic value is 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 stock options exercised during the three months ended March 31, 2017 was $1.4 million. There were no options exercised during the three months ended March 31, 2018. As of March 31, 2018, there was $7.2 million of total unrecognized stock-based compensation expense related to unvested employee stock awards. The Company expects to recognize this expense over a weighted-average period of approximately 2.58 years.

Net Loss Per Common Share

Net Loss Per Common Share	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Net Loss Per Common Share	7. Net Loss Per Common Share Basic net loss per share is calculated by dividing the net loss attributable to Merrimack Pharmaceuticals, Inc. by the weighted-average number of common shares outstanding during the period. Diluted net loss per share is computed by dividing the net loss attributable to Merrimack Pharmaceuticals, Inc. by the weighted-average number of dilutive common shares outstanding during the period. Dilutive shares outstanding is calculated by adding to the weighted shares outstanding any potential (unissued) shares of common stock from outstanding stock options based on the treasury stock method. In a period when a net loss is reported, all common stock equivalents are excluded from the calculation because they would have an anti-dilutive effect, meaning the loss per share would be reduced. Therefore, in periods where a loss is reported, there is no difference in basic and dilutive loss per share. The Company follows the two-class method when computing net loss per share when it has issued shares that meet the definition of participating securities. The two-class method determines net loss per share for each class of common and participating securities according to dividends declared or accumulated and participating rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based on their respective rights to receive dividends, as if all income for the period has been distributed or losses to be allocated if they are contractually required to fund losses. There were no amounts allocated to participating securities for the three months ended March 31, 2018 and 2017, as the Company was in a loss position and had no shares that met the definition of participating securities outstanding as of March 31, 2018 and 2017. The stock options and conversion premium on the 4.50% convertible notes due 2020 (the “Convertible Notes”) are excluded from the calculation of diluted loss per share because the net loss for the three months ended March 31, 2017 causes such securities to be anti-dilutive. Outstanding securities excluded from the calculation of diluted loss per share for the three months ended March 31, 2018 and 2017 are shown in the chart below: Three Months Ended March 31, (in thousands) 2018 2017 Outstanding options to purchase common stock 2,037 1,652 Conversion of the Convertible Notes — 1,216

Discontinued Operations

Discontinued Operations	3 Months Ended
	Mar. 31, 2018
Discontinued Operations And Disposal Groups [Abstract]
Discontinued Operations	8. Discontinued Operations On April 3, 2017, the Company completed the sale of the Commercial Business. As of March 31, 2017, the Commercial Business met all the conditions to be classified as a discontinued operation since the disposal of the Commercial Business represented a strategic shift that had a major effect on the Company’s operations and financial results. The condensed consolidated financial statements for the three months ended March 31, 2017 reflect the operations of the Commercial Business as a discontinued operation. Discontinued operations for the three months ended March 31, 2017 includes the following: (in thousands) Three Months Ended March 31, 2017 Revenues: Product revenues, net $ 16,135 License and collaboration revenues 7,797 Other revenues 1,973 Total revenues 25,905 Costs and expenses: Cost of revenues 3,890 Research and development expenses 3,730 Selling, general and administrative expenses 8,733 Restructuring expenses 5,265 Total costs and expenses 21,618 Other income and expenses: Interest expense (5,234 ) Loss from discontinued operations $ (947 ) On January 8, 2017, the Company announced a reduction in headcount by approximately 30% in connection with the sale of the Commercial Business and the completion of its strategic pipeline review. Under this corporate restructuring, for the three months ended March 31, 2017, the Company recognized total restructuring expenses of $5.3 million related to contractual termination benefits for employees with pre-existing severance arrangements. These one-time employee termination benefits are comprised of severance, benefits and related costs, all of which resulted in cash expenditures. The expense of $5.3 million was included in discontinued operations, as the costs are directly associated with the sale of the Commercial Business. For the three months ended March 31, 2018, there were no discontinued operations.

Investment in Silver Creek

Investment in Silver Creek	3 Months Ended
	Mar. 31, 2018
Noncontrolling Interest [Abstract]
Investment in Silver Creek	9. Investment in Silver Creek On August 20, 2010, the Company acquired a controlling financial interest in Silver Creek. At such time, the Company had the ability to direct the activities of Silver Creek that most significantly impacted Silver Creek’s economic performance through its ownership percentage and through the board of director seats controlled by the Company. As such, Silver Creek was consolidated by the Company. Since the Company acquired its financial interest, Silver Creek has raised funding through the issuance of preferred stock. The Company has not participated in any Silver Creek financings nor has it provided any funding. During the third quarter of 2017, Silver Creek completed its Series C preferred stock financing, reducing the Company’s ownership percentage in Silver Creek below 50% and resulting in the Company no longer controlling the Silver Creek board of directors. Accordingly, the Company determined that it was no longer the primary beneficiary of Silver Creek and deconsolidated Silver Creek from its financial statements on July 13, 2017. Starting on July 14, 2017, the Company accounted for its investment in Silver Creek under the equity method of accounting since the Company has the ability to exercise significant influence over Silver Creek. Under the equity method of accounting, the Company has recorded its proportionate share of the investee’s earnings (losses) in its results of operations with a corresponding increase (decrease) in the carrying value of the investment. Silver Creek continues to be a related party to the Company after deconsolidation.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	3 Months Ended
	Mar. 31, 2018
Accounting Changes And Error Corrections [Abstract]
Recent Accounting Pronouncements	10. Recent Accounting Pronouncements The Financial Accounting Standards Board (“FASB”) issued the following new Accounting Standards Updates (“ASU”), which the Company adopted on January 1, 2018: • ASU 2014-09, “Revenue from Contracts with Customers (Topic 606)” and related amendments; • ASU 2016-01, “Financial Instruments – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Liabilities”; • ASU 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments”; • ASU 2016-18, “Statement of Cash Flows - Restricted Cash (a consensus of the FASB Emerging Issues Task Force)”; and • ASU 2017-09, “Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting.” The adoption of these standards did not have a material impact on the Company’s financial position, results of operations or statement of cash flows; however, the adoption of ASU 2016-18 resulted in the reclassification of certain prior year amounts in the Company’s condensed consolidated statements of cash flows to conform to the current year presentation. In February 2016, the FASB issued ASU 2016-02, “Leases (Topic 842),” which supersedes all existing lease accounting guidance within ASC 840, Leases In June 2016, the FASB issued ASU 2016-13, “Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments,” which represents a new credit loss standard that will change the impairment model for most financial assets and certain other financial instruments. Specifically, this guidance will require entities to utilize a new “expected loss” model as it relates to trade and other receivables. In addition, entities will be required to recognize an allowance for estimated credit losses on available-for-sale debt securities, regardless of the length of time that a security has been in an unrealized loss position. This guidance will be effective for annual reporting periods beginning after December 15, 2019, including interim periods within those annual reporting periods, and early adoption is permitted. The Company is currently evaluating the potential impact that the adoption of this guidance may have on the condensed consolidated financial statements. In February 2018, the FASB issued ASU 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220)”. ASU 2018-02 addresses the effect of the change in the U.S. federal corporate tax rate due to the enactment of the December 22, 2017 Tax Cuts and Jobs Act (the “Tax Act”) on items within accumulated other comprehensive loss. The guidance will be effective for the Company in the first quarter of fiscal 2020 with early adoption permitted. The Company is currently assessing the impact that adopting this new accounting standard will have on the condensed consolidated financial statements. From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that the Company adopts as of the specified effective date. Unless otherwise discussed above, the Company does not believe that the adoption of recently issued standards has or may have a material impact on the Company’s condensed consolidated financial statements or disclosures.

Summary of Significant Accoun16

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements reflect the operations of Merrimack Pharmaceuticals, Inc. and its wholly owned subsidiary. All intercompany accounts and transactions have been eliminated. The condensed consolidated financial statements are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accounting policies followed in the preparation of the interim condensed consolidated financial statements are consistent in all material respects with those presented in Note 1 to the financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017. Certain reclassifications have been made to the prior year’s condensed consolidated balance sheet and condensed consolidated statement of cash flows to enhance comparability with the current year’s condensed consolidated financial statements presentation. These reclassifications had no effect on previously reported net income within the condensed consolidated statement of operations and comprehensive loss.
Consolidation	Consolidation The accompanying condensed consolidated financial statements reflect Merrimack Pharmaceuticals, Inc. and its wholly owned subsidiary. For the three months ended March 31, 2017, the condensed consolidated financial statements also include the accounts of Silver Creek Pharmaceuticals, Inc. (“Silver Creek”). For the three months ended March 31, 2017, Silver Creek represented a variable interest entity that the Company consolidated as the primary beneficiary. In the third quarter of 2017, the Company deconsolidated Silver Creek from its financial statements since the Company was no longer the primary beneficiary of Silver Creek. The Company’s ownership percentage decreased to less than 50% and the Company no longer controlled Silver Creek’s board of directors or directed the activities that had the most significant impact on Silver Creek’s economic performance. The Company accounts for its investment in Silver Creek under the equity method of accounting. On April 3, 2017, the Company completed the sale of its right, title and interest in the non-cash assets, equipment, inventory, contracts and intellectual property primarily related to developing, manufacturing and commercializing ONIVYDE and MM-436 (the “Commercial Business”). As of March 31, 2017, the Commercial Business met all the conditions to be classified as a discontinued operation since the disposal of the Commercial Business represented a strategic shift that had a major effect on the Company’s operations and financial results. Therefore, the operating results of the Commercial Business are reported as a loss from discontinued operations, net of tax in the condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2017. During the three months ended March 31, 2018, there were no discontinued operations.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The condensed consolidated balance sheet as of December 31, 2017 was derived from audited financial statements, but does not include all disclosures required by GAAP. The condensed consolidated balance sheet as of March 31, 2018, the condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2018 and 2017 and the condensed consolidated statements of cash flows for the three months ended March 31, 2018 and 2017 are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of March 31, 2018, the results of its operations for the three months ended March 31, 2018 and 2017, and its statements of cash flows for the three months ended March 31, 2018 and 2017. The financial data and other information disclosed in the notes related to the three months ended March 31, 2018 and 2017 are unaudited. The results for the three months ended March 31, 2018 and 2017 are not necessarily indicative of results to be expected for the year ending December 31, 2018, any other interim periods, or any future year or period. The unaudited interim financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”). Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements and the notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 filed with the SEC on March 12, 2018.
Condensed Consolidated Statements of Cash Flows	Condensed Consolidated Statements of Cash Flows The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the statement of financial position that sum to the total of the same such amounts shown in the statement of cash flows: (in thousands) March 31, 2018 March 31, 2017 Cash and cash equivalents $ 34,268 $ 17,155 Restricted cash in prepaid expenses and other current assets 102 — Restricted cash (short term) — 102 Restricted cash (long term) 674 674 Total cash, cash equivalents and restricted cash shown in the condensed consolidated statement of cash flows $ 35,044 $ 17,931 Restricted cash included in prepaid expenses and other current assets and restricted cash long term on the statement of financial position represent amounts pledged as collateral for operating lease obligations as contractually required. This restriction will lapse when the arrangements expire.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates, assumptions and judgments that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements and the reported amounts of revenue and expenses during the reporting periods. Significant estimates, assumptions and judgments reflected in these condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.
Marketable Securities	Marketable Securities Marketable securities consist of investments with original maturities greater than ninety days. The Company has classified its investments with maturities beyond one year as short term based on their highly liquid nature and because such marketable securities represent the investment of cash that is available for current operations. The Company considers its investment portfolio of marketable debt securities as available-for-sale. Accordingly, these marketable debt securities are recorded at fair value and unrealized gains and losses are reported as a component of accumulated other comprehensive loss in stockholders’ equity. Realized gains and losses and declines in value judged to be other than temporary are included as a component of other income (expense), net based on the specific identification method. When determining whether a decline in value is other than temporary, the Company considers various factors, including whether the Company has the intent to sell the security, and whether it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis.
Recent Accounting Pronouncements	The Financial Accounting Standards Board (“FASB”) issued the following new Accounting Standards Updates (“ASU”), which the Company adopted on January 1, 2018: • ASU 2014-09, “Revenue from Contracts with Customers (Topic 606)” and related amendments; • ASU 2016-01, “Financial Instruments – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Liabilities”; • ASU 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments”; • ASU 2016-18, “Statement of Cash Flows - Restricted Cash (a consensus of the FASB Emerging Issues Task Force)”; and • ASU 2017-09, “Compensation - Stock Compensation (Topic 718): Scope of Modification Accounting.” The adoption of these standards did not have a material impact on the Company’s financial position, results of operations or statement of cash flows; however, the adoption of ASU 2016-18 resulted in the reclassification of certain prior year amounts in the Company’s condensed consolidated statements of cash flows to conform to the current year presentation. In February 2016, the FASB issued ASU 2016-02, “Leases (Topic 842),” which supersedes all existing lease accounting guidance within ASC 840, Leases In June 2016, the FASB issued ASU 2016-13, “Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments,” which represents a new credit loss standard that will change the impairment model for most financial assets and certain other financial instruments. Specifically, this guidance will require entities to utilize a new “expected loss” model as it relates to trade and other receivables. In addition, entities will be required to recognize an allowance for estimated credit losses on available-for-sale debt securities, regardless of the length of time that a security has been in an unrealized loss position. This guidance will be effective for annual reporting periods beginning after December 15, 2019, including interim periods within those annual reporting periods, and early adoption is permitted. The Company is currently evaluating the potential impact that the adoption of this guidance may have on the condensed consolidated financial statements. In February 2018, the FASB issued ASU 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220)”. ASU 2018-02 addresses the effect of the change in the U.S. federal corporate tax rate due to the enactment of the December 22, 2017 Tax Cuts and Jobs Act (the “Tax Act”) on items within accumulated other comprehensive loss. The guidance will be effective for the Company in the first quarter of fiscal 2020 with early adoption permitted. The Company is currently assessing the impact that adopting this new accounting standard will have on the condensed consolidated financial statements. From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies that the Company adopts as of the specified effective date. Unless otherwise discussed above, the Company does not believe that the adoption of recently issued standards has or may have a material impact on the Company’s condensed consolidated financial statements or disclosures.

Summary of Significant Accoun17

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash	The following table provides a reconciliation of cash, cash equivalents and restricted cash reported within the statement of financial position that sum to the total of the same such amounts shown in the statement of cash flows: (in thousands) March 31, 2018 March 31, 2017 Cash and cash equivalents $ 34,268 $ 17,155 Restricted cash in prepaid expenses and other current assets 102 — Restricted cash (short term) — 102 Restricted cash (long term) 674 674 Total cash, cash equivalents and restricted cash shown in the condensed consolidated statement of cash flows $ 35,044 $ 17,931

Fair Value of Financial Instr18

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Summary 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 March 31, 2018 and December 31, 2017: March 31, 2018 (in thousands) Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 6,785 $ — $ — Corporate debt securities — 2,009 — Commercial paper — 13,781 — Totals $ 6,785 $ 15,790 $ — Marketable securities: Corporate debt securities $ — $ 6,217 $ — Commercial paper — 21,841 — Government securities — 13,940 — Totals $ — $ 41,998 $ — December 31, 2017 (in thousands) Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 89,310 $ — $ — Totals $ 89,310 $ — $ —

Marketable Securities and Cas19

Marketable Securities and Cash Equivalents (Tables)	3 Months Ended
	Mar. 31, 2018
Investments Debt And Equity Securities [Abstract]
Summary of Marketable Securities and Cash Equivalents	The following table summarizes the Company’s marketable securities and cash equivalents as of March 31, 2018. The Company did not hold any marketable securities as of December 31, 2017. March 31, 2018 (in thousands) Amortized Cost Unrealized Losses Fair Value Cash equivalents: Money market funds $ 6,785 $ — $ 6,785 Corporate debt securities 2,010 (1 ) 2,009 Commercial paper 13,781 — 13,781 Total cash equivalents $ 22,576 $ (1 ) $ 22,575 Marketable securities: Corporate debt securities $ 6,227 $ (10 ) $ 6,217 Commercial paper 21,841 — 21,841 Government securities 13,941 (1 ) 13,940 Total marketable securities $ 42,009 $ (11 ) $ 41,998 Total cash equivalents and marketable securities $ 64,585 $ (12 ) $ 64,573

Accounts Payable, Accrued Exp20

Accounts Payable, Accrued Expenses and Other (Tables)	3 Months Ended
	Mar. 31, 2018
Payables And Accruals [Abstract]
Schedule of Accounts Payable, Accrued Expenses and Other	Accounts payable, accrued expenses and other as of March 31, 2018 and December 31, 2017 consisted of the following: (in thousands) March 31, 2018 December 31, 2017 Accounts payable $ 2,560 $ 2,887 Accrued goods and services 4,027 5,682 Accrued clinical trial costs 4,925 3,901 Accrued drug purchase costs 918 222 Accrued payroll and related benefits 1,240 2,884 Accrued restructuring expenses 251 628 Deferred tax incentives 1,402 1,402 Total accounts payable, accrued expenses and other $ 15,323 $ 17,606

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Assumptions Used to Calculate Fair Value of Options Granted to Employees	The fair value of stock options granted to employees during the three months ended March 31, 2018 and 2017 was estimated at the date of grant using the following assumptions: Three Months Ended March 31, 2018 2017 Risk-free interest rate 2.3 – 2.7% 2.1 % Expected dividend yield 0% 0% Expected term 5.8 years 5.8 years Expected volatility 62 – 63% 67 – 68%
Schedule of Recognized Stock-Based Compensation Expense	The Company recognized stock-based compensation expense during the three months ended March 31, 2018 and 2017 as follows: Three Months Ended March 31, (in thousands) 2018 2017 Employee awards: Research and development expense $ 334 $ 468 General and administrative expense 430 328 Total stock-based compensation expense $ 764 $ 796
Summary of Stock Option Activity	The following table summarizes stock option activity during the three months ended March 31, 2018: Weighted-Average Remaining Aggregate (in thousands, except per share amounts) Options Weighted-Average Exercise Price Contractual Term (in years) Intrinsic Value Outstanding at December 31, 2017 1,616 $ 22.07 6.65 $ 60,031 Granted 566 $ 10.74 Exercised — $ — Forfeited (145 ) $ 21.04 Outstanding at March 31, 2018 2,037 $ 19.00 7.22 $ — Vested and expected to vest at March 31, 2018 2,036 $ 19.00 7.22 $ — Exercisable at March 31, 2018 1,032 $ 25.17 4.97 $ —

Net Loss Per Common Share (Tabl

Net Loss Per Common Share (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Schedule of Outstanding Securities Excluded from Computation of Diluted Loss Per Share	Outstanding securities excluded from the calculation of diluted loss per share for the three months ended March 31, 2018 and 2017 are shown in the chart below: Three Months Ended March 31, (in thousands) 2018 2017 Outstanding options to purchase common stock 2,037 1,652 Conversion of the Convertible Notes — 1,216

Discontinued Operations (Tables

Discontinued Operations (Tables)	3 Months Ended
	Mar. 31, 2018
Discontinued Operations And Disposal Groups [Abstract]
Schedule of Discontinued Operations	Discontinued operations for the three months ended March 31, 2017 includes the following: (in thousands) Three Months Ended March 31, 2017 Revenues: Product revenues, net $ 16,135 License and collaboration revenues 7,797 Other revenues 1,973 Total revenues 25,905 Costs and expenses: Cost of revenues 3,890 Research and development expenses 3,730 Selling, general and administrative expenses 8,733 Restructuring expenses 5,265 Total costs and expenses 21,618 Other income and expenses: Interest expense (5,234 ) Loss from discontinued operations $ (947 )

Nature of the Business - Additi

Nature of the Business - Additional Information (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)Program	Mar. 31, 2017USD ($)	Dec. 31, 2017USD ($)
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of development programs active | Program	2
Accumulated deficit	$ 500,553		$ 482,771
Net loss from continuing operations	17,782	$ 29,206
Cash in continuing operations for operating activities	17,339	$ 18,124
Cash and cash equivalents and marketable securities	$ 76,300

Summary of Significant Accoun25

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Summary Of Significant Accounting Policies [Line Items]
Discontinued operations	$ 0	$ (947,000)
Maximum [Member] | Silver Creek Pharmaceuticals Inc [Member]
Summary Of Significant Accounting Policies [Line Items]
Ownership interest (as a percent)			50.00%

Summary of Significant Accoun26

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Cash Cash Equivalents And Restricted Cash [Line Items]
Cash and cash equivalents	$ 34,268	$ 93,441	$ 17,155
Restricted cash (short term)			102
Restricted cash (long term)	674		674
Total cash, cash equivalents and restricted cash shown in the condensed consolidated statement of cash flows	35,044	$ 94,217	$ 17,931	$ 22,300
Prepaid Expenses and Other Current Assets [Member]
Cash Cash Equivalents And Restricted Cash [Line Items]
Restricted cash (short term)	$ 102

Fair Value of Financial Instr27

Fair Value of Financial Instruments - Summary of Assets Measured at Fair Value on a Recurring Basis (Detail) - Recurring Basis [Member] - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	$ 6,785	$ 89,310
Level 1 [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	6,785	$ 89,310
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	15,790
Marketable securities	41,998
Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	2,009
Marketable securities	6,217
Level 2 [Member] | Commercial Paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	13,781
Level 2 [Member] | Commercial Paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	21,841
Level 2 [Member] | Government Securites [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	$ 13,940

Fair Value of Financial Instr28

Fair Value of Financial Instruments - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Fair value transfers between Level 1 and Level 2	no	no

Marketable Securities and Cas29

Marketable Securities and Cash Equivalents - Additional Information (Detail)	Dec. 31, 2017USD ($)
Amortized Cost And Fair Value Debt Securities [Abstract]
Marketable securities	$ 0

Marketable Securities and Cas30

Marketable Securities and Cash Equivalents - Summary of Marketable Securities and Cash Equivalents (Detail) $ in Thousands	Mar. 31, 2018USD ($)
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 64,585
Unrealized Losses	(12)
Fair Value	64,573
Cash Equivalents [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	22,576
Unrealized Losses	(1)
Fair Value	22,575
Cash Equivalents [Member] | Money Market Funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	6,785
Fair Value	6,785
Cash Equivalents [Member] | Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	2,010
Unrealized Losses	(1)
Fair Value	2,009
Cash Equivalents [Member] | Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	13,781
Fair Value	13,781
Marketable Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	42,009
Unrealized Losses	(11)
Fair Value	41,998
Marketable Securities [Member] | Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	6,227
Unrealized Losses	(10)
Fair Value	6,217
Marketable Securities [Member] | Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	21,841
Fair Value	21,841
Marketable Securities [Member] | Government Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	13,941
Unrealized Losses	(1)
Fair Value	$ 13,940

Accounts Payable, Accrued Exp31

Accounts Payable, Accrued Expenses and Other - Schedule of Accounts Payable, Accrued Expenses and Other (Detail) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accounts payable	$ 2,560	$ 2,887
Accrued goods and services	4,027	5,682
Accrued clinical trial costs	4,925	3,901
Accrued drug purchase costs	918	222
Accrued payroll and related benefits	1,240	2,884
Accrued restructuring expenses	251	628
Deferred tax incentives	1,402	1,402
Total accounts payable, accrued expenses and other	$ 15,323	$ 17,606

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Options, Granted	566
Weighted-average grant date fair value per share of stock options	$ 6.26	$ 24.30
Aggregate intrinsic value of options exercised	$ 0	$ 1.4
Unrecognized stock-based compensation expense related to nonvested stock awards	$ 7.2
Weighted average period over which unrecognized stock-based compensation expense is expected to be recognized	2 years 6 months 29 days
Stock Incentive Plan 2011 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock available for grant (in shares)	500
Number of Options, Granted	600	0
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 - Sche

Stock-Based Compensation - Schedule of Assumptions Used to Calculate Fair Value of Options Granted to Employees (Detail) - Options to Purchase Common Stock [Member]	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate		2.10%
Expected dividend yield	0.00%	0.00%
Expected term	5 years 9 months 18 days	5 years 9 months 18 days
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.30%
Expected volatility	62.00%	67.00%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.70%
Expected volatility	63.00%	68.00%

Stock-Based Compensation - Sc34

Stock-Based Compensation - Schedule of Recognized Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 764	$ 796
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense for employee awards	334	468
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense for employee awards	$ 430	$ 328

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding Roll Forward
Number of Options, Outstanding, Beginning balance	1,616
Number of Options, Granted	566
Number of Options, Forfeited	(145)
Number of Options, Outstanding, Ending balance	2,037	1,616
Number of Options, Vested and expected to vest	2,036
Number of Options, Exercisable	1,032
Weighted-Average Exercise Price, Outstanding, Beginning balance	$ 22.07
Weighted-Average Exercise Price, Granted	10.74
Weighted-Average Exercise Price, Forfeited	21.04
Weighted-Average Exercise Price, Outstanding, Ending balance	19	$ 22.07
Weighted-Average Exercise Price, Vested and expected to vest	19
Weighted-Average Exercise Price, Exercisable	$ 25.17
Weighted-Average Remaining Contractual Term	7 years 2 months 19 days	6 years 7 months 24 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	7 years 2 months 19 days
Weighted-Average Remaining Contractual Term, Exercisable	4 years 11 months 19 days
Aggregate Intrinsic Value, Outstanding		$ 60,031

Net Loss Per Common Share - Add

Net Loss Per Common Share - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Amounts allocated to participating securities	$ 0	$ 0
Participating securities outstanding, shares	0	0
Convertible Notes [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Interest rate (as a percent)	4.50%

Net Loss Per Common Share - Sch

Net Loss Per Common Share - Schedule of Outstanding Securities Excluded from Computation of Diluted Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Outstanding Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding securities excluded from calculation of diluted loss per share	2,037	1,652
Conversion of the Convertible Notes [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Outstanding securities excluded from calculation of diluted loss per share		1,216

Discontinued Operations - Sched

Discontinued Operations - Schedule of Discontinued Operations (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Other income and expenses:
Loss from discontinued operations	$ 0	$ (947,000)
Commercial Business [Member]
Revenues:
Product revenues, net		16,135,000
License and collaboration revenues		7,797,000
Other revenues		1,973,000
Total revenues		25,905,000
Costs and expenses:
Cost of revenues		3,890,000
Research and development expenses		3,730,000
Selling, general and administrative expenses		8,733,000
Restructuring expenses		5,265,000
Total costs and expenses		21,618,000
Other income and expenses:
Interest expense		(5,234,000)
Loss from discontinued operations		$ (947,000)

Discontinued Operations - Addit

Discontinued Operations - Additional Information (Detail) - USD ($)	Jan. 08, 2017	Mar. 31, 2018	Mar. 31, 2017
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Discontinued operations		$ 0	$ (947,000)
January 2017 Corporate Restructuring [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Restructuring activity, announcement date		Jan. 8, 2017
Reduction in headcount, percent	30.00%
January 2017 Corporate Restructuring [Member] | Discontinued Operations [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Restructuring expenses		$ 5,300,000
January 2017 Corporate Restructuring [Member] | Contractual Termination Benefits [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Restructuring expenses		$ 5,300,000
January 2017 Corporate Restructuring [Member] | One-time Employee Termination Benefits [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Restructuring activities, description		One-time employee termination benefits are comprised of severance, benefits and related costs, all of which are expected to result in cash expenditures. The majority of these payments were made during the second quarter of 2017. The remaining payments represent severance payments that will be paid over one year.

Investment in Silver Creek - Ad

Investment in Silver Creek - Additional Information (Detail)	Sep. 30, 2017
Silver Creek Pharmaceuticals Inc [Member] | Maximum [Member]
Consolidation Less Than Wholly Owned Subsidiary Parent Ownership Interest Effects Of Changes Net [Line Items]
Ownership interest percentage held by parent	50.00%