Merrimack Pharmaceuticals (MACK) 10-Q 12 Nov 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Nov. 08, 2019
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Trading Symbol	MACK
Entity Registrant Name	MERRIMACK PHARMACEUTICALS INC
Entity Central Index Key	0001274792
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		13,362,951
Entity Shell Company	false
Entity File Number	001-35409
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-3210530
Entity Address, Address Line One	One Broadway, 14th Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02142
City Area Code	617
Local Phone Number	441-1000
Document Quarterly Report	true
Document Transition Report	false
Title of 12(b) Security	Common stock, $0.01 par value
Security Exchange Name	NASDAQ

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 20,858	$ 20,079
Marketable securities		51,199
Restricted cash		584
Prepaid expenses and other current assets	1,540	4,240
Total current assets	22,398	76,102
Property and equipment, net		2,269
Equity method investment		7,428
Other assets	2,443	2,744
Total assets	24,841	88,543
Current liabilities:
Accounts payable, accrued expenses and other	4,683	13,677
Deferred rent		1,118
Other current liabilities	56
Total current liabilities	4,739	14,795
Note payable, net of discount and current portion		14,873
Other long-term liabilities		56
Total liabilities	4,739	29,724
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.01 par value: 10,000 shares authorized at September 30, 2019 and December 31, 2018; no shares issued or outstanding at September 30, 2019 or December 31, 2018
Common stock, $0.01 par value: 30,000 shares authorized at September 30, 2019 and December 31, 2018; 13,363 and 13,343 shares issued and outstanding at September 30, 2019 and December 31, 2018, respectively	1,334	1,334
Additional paid-in capital	562,638	580,771
Accumulated other comprehensive loss		(9)
Accumulated deficit	(543,870)	(523,277)
Total stockholders’ equity	20,102	58,819
Total liabilities and stockholders’ equity	$ 24,841	$ 88,543

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
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	30,000,000	30,000,000
Common stock, shares issued	13,363,000	13,343,000
Common stock, shares outstanding	13,363,000	13,343,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	Dec. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Operating expenses:
Research and development expenses		$ 12,959	$ 11,100	$ 39,743
General and administrative expenses	$ 4,346	3,777	13,958	11,560
Gain on sale of assets	(3,500)		(4,910)
Total operating expenses	846	16,736	20,148	51,303
Loss from operations	(846)	(16,736)	(20,148)	(51,303)
Other income and expenses:
Interest income	140	306	712	863
Interest expense		(472)	(1,527)	(472)
Other (expense) income, net	1	(237)	370	(1,778)
Total other income and expenses	141	(403)	(445)	(1,387)
Net loss from continuing operations before income tax benefit	(705)	(17,139)	(20,593)	(52,690)
Income tax benefit		4,798		4,798
Net loss from continuing operations	(705)	(12,341)	(20,593)	(47,892)
Discontinued operations:
Income from discontinued operations, net of tax		16,330		16,330
Net income (loss)	(705)	3,989	(20,593)	(31,562)
Other comprehensive income (loss):
Unrealized gain (loss) on marketable securities		(4)	9	(5)
Other comprehensive income (loss)		(4)	9	(5)
Comprehensive income (loss)	$ (705)	$ 3,985	$ (20,584)	$ (31,567)
Basic and dilutive net income (loss) per common share:
Net loss from continuing operations	$ (0.05)	$ (0.92)	$ (1.54)	$ (3.59)
Net income from discontinued operations, net of tax		1.22		1.22
Net income (loss) per share	$ (0.05)	$ 0.30	$ (1.54)	$ (2.37)
Weighted-average common shares used to compute basic and diluted net loss per common share	13,358	13,343	13,348	13,343
Cash dividend paid per common share	$ 1.4967

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2017	$ 96,284	$ 1,334	$ 577,721		$ (482,771)
Balance (in shares) at Dec. 31, 2017		13,343
Stock-based compensation	764		764
Unrealized gain (loss) on marketable securities	(12)			$ (12)
Net income (loss)	(17,782)				(17,782)
Balance at Mar. 31, 2018	79,254	$ 1,334	578,485	(12)	(500,553)
Balance (in shares) at Mar. 31, 2018		13,343
Balance at Dec. 31, 2017	96,284	$ 1,334	577,721		(482,771)
Balance (in shares) at Dec. 31, 2017		13,343
Unrealized gain (loss) on marketable securities	(5)
Net income (loss)	(31,562)
Balance at Sep. 30, 2018	67,043	$ 1,334	580,047	(5)	(514,333)
Balance (in shares) at Sep. 30, 2018		13,343
Balance at Mar. 31, 2018	79,254	$ 1,334	578,485	(12)	(500,553)
Balance (in shares) at Mar. 31, 2018		13,343
Stock-based compensation	780		780
Unrealized gain (loss) on marketable securities	11			11
Net income (loss)	(17,769)				(17,769)
Balance at Jun. 30, 2018	62,276	$ 1,334	579,265	(1)	(518,322)
Balance (in shares) at Jun. 30, 2018		13,343
Stock-based compensation	782		782
Unrealized gain (loss) on marketable securities	(4)			(4)
Net income (loss)	3,989				3,989
Balance at Sep. 30, 2018	67,043	$ 1,334	580,047	(5)	(514,333)
Balance (in shares) at Sep. 30, 2018		13,343
Balance at Dec. 31, 2018	58,819	$ 1,334	580,771	(9)	(523,277)
Balance (in shares) at Dec. 31, 2018		13,343
Stock-based compensation	594		594
Unrealized gain (loss) on marketable securities	9			9
Net income (loss)	(10,458)				(10,458)
Balance at Mar. 31, 2019	48,964	$ 1,334	581,365		(533,735)
Balance (in shares) at Mar. 31, 2019		13,343
Balance at Dec. 31, 2018	58,819	$ 1,334	580,771	$ (9)	(523,277)
Balance (in shares) at Dec. 31, 2018		13,343
Unrealized gain (loss) on marketable securities	9
Net income (loss)	(20,593)
Balance at Sep. 30, 2019	20,102	$ 1,334	562,638		(543,870)
Balance (in shares) at Sep. 30, 2019		13,363
Balance at Mar. 31, 2019	48,964	$ 1,334	581,365		(533,735)
Balance (in shares) at Mar. 31, 2019		13,343
Stock-based compensation	487		487
Exercise of stock options	23		23
Exercise of stock options (in shares)		6
Net income (loss)	(9,430)				(9,430)
Balance at Jun. 30, 2019	40,044	$ 1,334	581,875		(543,165)
Balance (in shares) at Jun. 30, 2019		13,349
Stock-based compensation	703		703
Exercise of stock options	60		60
Exercise of stock options (in shares)		14
Dividend paid	(20,000)		(20,000)
Net income (loss)	(705)				(705)
Balance at Sep. 30, 2019	$ 20,102	$ 1,334	$ 562,638		$ (543,870)
Balance (in shares) at Sep. 30, 2019		13,363

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net loss	$ (20,593)	$ (31,562)
Gain from discontinued operations		16,330
Loss from continuing operations	(20,593)	(47,892)
Adjustments to reconcile net loss to net cash used in operating activities
Non-cash interest expense	141	121
Loss on extinguishment of debt	971
Benefit from intraperiod tax allocation		(4,798)
Depreciation and amortization expense	2,228	3,211
Non-cash activity related to discontinued operations		(532)
Loss (gain) on sale of equipment	(1,984)	184
Gain on sale of in progress research and development asset	(3,500)
Premiums paid on marketable securities		(2)
Amortization and accretion on marketable securities	(292)	(398)
Stock-based compensation expense	1,784	2,326
Loss (gain) on equity method investment	(372)	1,658
Changes in operating assets and liabilities:
Prepaid expenses and other assets	3,001	(314)
Income taxes payable		361
Accounts payable, accrued expenses and other	(10,112)	1,083
Deferred rent		(1,704)
Net cash used in operating activities	(28,728)	(46,696)
Cash flows from investing activities
Purchase of property and equipment		(118)
Proceeds from sale of equipment	2,025
Proceeds from sale of in progress research and development asset	3,500
Proceeds from sale of equity method investment	7,800
Proceeds from sale of business		23,000
Proceeds from maturities and sales of marketable securities	51,500	42,200
Purchases of marketable securities		(76,857)
Net cash provided by (used in) investing activities	64,825	(11,775)
Cash flows from financing activities
Proceeds from issuance of notes payable, net of issuance costs		14,632
Proceeds from exercise of stock options	83
Repayment of debt	(15,000)
Payment of debt extinguishment costs	(985)
Payment of dividend	(20,000)
Net cash (used in) provided by financing activities	(35,902)	14,632
Net increase (decrease) in cash, cash equivalents and restricted cash	195	(43,839)
Cash, cash equivalents and restricted cash, beginning of period	20,663	94,217
Cash, cash equivalents and restricted cash, end of period	20,858	50,378
Supplemental disclosure of cash flows
Cash paid for interest	$ 1,399	$ 235

Nature of the Business

Nature of the Business	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business Merrimack Pharmaceuticals, Inc. (the “Company”) is a biopharmaceutical company based in Cambridge, Massachusetts that is entitled to receive up to $455.0 million in contingent milestone payments related to its sale of ONIVYDE ® On April 3, 2017, the Company completed the sale to Ipsen (the “Ipsen Sale”) of ONIVYDE and MM-436. In connection with the Ipsen Sale, the Company is eligible to receive up to $450.0 million in additional regulatory approval-based milestone payments. The Company is also eligible to receive a remaining $5.0 million milestone payment that may become payable for the ex-U.S. development and commercialization of ONIVYDE pursuant to a license and collaboration agreement (the “Servier Agreement”) between Ipsen and Les Laboratoires Servier SAS (“Servier”) (as assignee from Shire plc). The Company entered into the Servier Agreement in 2014, and on April 3, 2017, the Servier Agreement was assigned to Ipsen in connection with the completion of the Ipsen Sale. To date, the Company has received $28.0 million of the potential $33.0 million in milestone payments under the Servier Agreement. The remaining up to $455.0 million in potential milestone payments resulting from the Ipsen Sale consist of: • $5.0 million upon Ipsen and Servier’s joint decision to progress their ongoing multi-part clinical trial evaluating ONIVYDE in small-cell lung cancer (“SCLC”) into the second randomized portion of the trial focused on efficacy; • $225.0 million upon approval by the U.S. Food and Drug Administration (“FDA”) of ONIVYDE for the first-line treatment of metastatic adenocarcinoma of the pancreas, subject to certain conditions; • $150.0 million upon approval by the FDA of ONIVYDE for the treatment of small-cell lung cancer (“SCLC”) after failure of first-line chemotherapy; and • $75.0 million upon approval by the FDA of ONIVYDE for an additional indication unrelated to those described above. On May 30, 2019, the Company announced the completion of its review of strategic alternatives, following which the Company’s board of directors implemented a series of measures designed to extend the Company’s cash runway and preserve its ability to capture the potential milestone payments resulting from the Ipsen Sale. In connection with that announcement, the Company discontinued the discovery efforts on its remaining preclinical programs: MM-401, an agonistic antibody targeting a novel immuno-oncology target, TNFR2; and MM-201, a highly stabilized agonist-Fc fusion protein targeting death receptors 4 and 5. The Company is seeking potential acquirers for its remaining preclinical and clinical assets. The Company’s termination of its executive management team and all other employees was substantially completed by June 28, 2019 and fully completed by July 12, 2019. As of July 12, 2019, the Company does not have any employees. The Company has engaged external consultants to run the day-to-day operations of the Company. The Company has also entered into consulting agreements with certain former members of its executive management team who are supporting the Company’s relationship with current partners, assisting with the potential sale of remaining preclinical and clinical assets, and assisting with certain legal matters and the continued wind-down of operations. In May 2019, the Company monetized certain assets to strengthen its cash position. This includes the sale of its entire equity position in Silver Creek Pharmaceuticals, Inc. (“Silver Creek”), resulting in $7.8 million in cash, and the sale of laboratory equipment from its research and development operations, resulting in approximately $1.4 million in cash. On April 15, 2019, the Company repaid in full all principal, accrued and unpaid interest, fees, costs and expenses under its Loan and Security Agreement (the “Loan Agreement”) with Hercules Capital, Inc. (“Hercules”) in an aggregate amount equal to $16.0 million. On July 12, 2019, the Company completed the sale to 14ner Oncology, Inc. (“14ner”) (the “14ner Sale”) of its anti-HER3 antibody programs, MM-121 (seribantumab) and MM-111. In connection with the 14ner Sale, the Company received an upfront cash payment of $3.5 million in connection with the completion of the 14ner Sale. The Company is also eligible to receive up to $54.5 million in additional potential development, regulatory approval and commercial-based milestone payments, consisting of: • $3.0 million for achievement of the primary endpoint in the first registrational clinical study of either MM-121 or MM-111; • Up to $16.5 million in total payments for the achievement of various regulatory approval and reimbursement-based milestones in the United States, Europe and Japan; and • Up to $35.0 million in total payments for achieving various cumulative worldwide net sales targets between $100.0 million and $300.0 million for MM-121 and MM-111. • The Company’s board of directors authorized and declared a special cash dividend of $20.0 million to holders of the Company's common stock, which was payable on September 5, 2019 to stockholders of record as of the close of business on August 28, 2019. 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, development by competitors of new technological innovations, protection of proprietary technology and compliance with government regulations. None of the Company’s product candidates are approved for any indication by the FDA or any other regulatory agency. 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 external consultants for the operation of the Company. The Company’s business strategy depends substantially upon its ability to receive future milestone payments from Ipsen and Servier. Any failure to achieve such milestones or a perception that the milestones may not be achieved will materially and adversely affect the Company and the value of its common stock. In accordance with Accounting Standards Codification (“ASC”) 205-40, Going Concern The Company expects that it would finance any future cash needs through a combination of divestitures of its product candidates or other assets, equity offerings and debt financings. There can be no assurance as to the timing, terms or consummation of any divestiture or financing, and the terms of any such financing may adversely affect the holdings or the rights of the Company’s stockholders or require the Company to relinquish rights to certain of its revenue streams or product candidates.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
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 subsidiaries. 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, 2018. Consolidation The accompanying condensed consolidated financial statements reflect Merrimack Pharmaceuticals, Inc. and its wholly owned subsidiaries. Unaudited Interim Financial Information The condensed consolidated balance sheet as of December 31, 2018 was derived from audited financial statements, but does not include all disclosures required by GAAP. The condensed consolidated balance sheet as of September 30, 2019, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2019 and 2018, the condensed consolidated statements of stockholders’ equity for the three and nine months ended September 30, 2019 and 2018 and the condensed consolidated statements of cash flows for the nine months ended September 30, 2019 and 2018 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 September 30, 2019, the results of its operations for the three and nine months ended September 30, 2019 and 2018, its statements of stockholders’ equity for the three and nine months ended September 30, 2019 and 2018 and its statements of cash flows for the nine months ended September 30, 2019 and 2018. The financial data and other information disclosed in the notes related to the three and nine months ended September 30, 2019 and 2018 are unaudited. The results for the three and nine months ended September 30, 2019 and 2018 are not necessarily indicative of results to be expected for the year ending December 31, 2019, 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, 2018 filed with the SEC on March 6, 2019. 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) September 30, 2019 September 30, 2018 Cash and cash equivalents $ 20,858 $ 49,794 Restricted cash (long-term) — 584 Total cash, cash equivalents and restricted cash shown in the condensed consolidated statement of cash flows $ 20,858 $ 50,378 Restricted cash on the statement of financial position for 2018 primarily represents amounts pledged as collateral for operating lease obligations as contractually required. 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 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.

Leases

Leases	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Leases	3. Leases The Company adopted the new leasing standards on January 1, 2019, using the modified retrospective transition method, which does not require restatement of prior periods, for all the leases existing as of the adoption date. The adoption of the new leasing standards did not have a significant impact on the Company’s consolidated financial statements. As of January 1, 2019, the Company’s only existing lease was the lease of its principal research and office space located at One Kendall Square in Cambridge, Massachusetts, which expired in June 2019.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	4. 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 September 30, 2019 and December 31, 2018: September 30, 2019 (in thousands) Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 16,705 $ — $ — Totals $ 16,705 $ — $ — December 31, 2018 (in thousands) Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 16,292 $ — $ — Commercial paper — 1,998 — Totals $ 16,292 $ 1,998 $ — Marketable securities: Commercial paper $ — $ 31,766 $ — Corporate debt securities — 7,479 — Government securities — 11,954 — Totals $ — $ 51,199 $ — During the nine months ended September 30, 2019 and the year ended December 31, 2018, 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 Company’s cash, restricted cash, prepaid expenses and other current assets, accounts payable and accrued expenses are recorded at cost, which approximates fair value due to their short-term nature.

Marketable Securities and Cash

Marketable Securities and Cash Equivalents	9 Months Ended
	Sep. 30, 2019
Investments Debt And Equity Securities [Abstract]
Marketable Securities and Cash Equivalents	5. Marketable Securities and Cash Equivalents The following table summarizes the Company’s marketable securities and cash equivalents as of September 30, 2019 and December 31, 2018: September 30, 2019 (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds $ 16,705 $ — $ — $ 16,705 Total cash equivalents $ 16,705 $ — $ — $ 16,705 December 31, 2018 (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds $ 16,292 $ — $ — $ 16,292 Commercial paper 1,998 — — 1,998 Total cash equivalents $ 18,290 $ — $ — $ 18,290 Marketable securities: Commercial paper $ 31,766 $ — $ — $ 31,766 Corporate debt securities 7,487 — (8 ) 7,479 Government securities 11,955 — (1 ) 11,954 Total marketable securities $ 51,208 $ — $ (9 ) $ 51,199

Notes Payable

Notes Payable	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Notes Payable	6. Notes Payable Through April 15, 2019, the Company borrowed $15.0 million under the Loan Agreement by and among the Company, certain subsidiaries of the Company from time to time party thereto, the several banks and other financial institutions or entities from time to time parties thereto (collectively referred to as “Lender”) and Hercules, in its capacity as administrative agent and collateral agent for itself and Lender, On April 15, 2019, the Company repaid in full all principal, accrued and unpaid interest, fees, costs and expenses under the Loan Agreement in an aggregate amount equal to $16.0 million (the “Payoff Amount”). The Payoff Amount includes a prepayment penalty of $0.2 million and a fee of $0.8 million, which were recorded to interest expense. The loss on extinguishment of the debt of approximately $1.0 million was recorded as interest expense during the second quarter of 2019. The loss on extinguishment represents the difference between the reacquisition price of the debt and the net carrying amount of the extinguished debt. In connection with the payment of the Payoff Amount, all liens and security interests granted to secure the obligations under the Loan Agreement and all guaranties of the obligations under the Loan Agreement terminated. No interest expense was associated with the Loan Agreement for the three months ended September 30, 2019. During the nine months ended September 30, 2019, the Company recognized $1.5 million of interest expense related to the Loan Agreement. No interest expense was associated with the Loan Agreement for the three and nine months ended September 30, 2018.

Accounts Payable, Accrued Expen

Accounts Payable, Accrued Expenses and Other	9 Months Ended
	Sep. 30, 2019
Payables And Accruals [Abstract]
Accounts Payable, Accrued Expenses and Other	7. Accounts Payable, Accrued Expenses and Other Accounts payable, accrued expenses and other as of September 30, 2019 and December 31, 2018 consisted of the following: (in thousands) September 30, 2019 December 31, 2018 Accounts payable $ 710 $ 1,034 Accrued goods and services 1,399 2,082 Accrued clinical trial costs 684 1,683 Accrued drug purchase costs 371 4,245 Accrued payroll and related benefits — 2,315 Accrued restructuring expenses 122 921 Income taxes payable 83 83 Deferred tax incentives 1,314 1,314 Total accounts payable, accrued expenses and other $ 4,683 $ 13,677

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	8. 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. The Company’s board of directors authorized and declared a special cash dividend of $20.0 million to holders of the Company's common stock, which was payable on September 5, 2019 to stockholders of record as of the close of business on August 28, 2019. The board of directors determined, in accordance with the adjustment provision of the 2011 Plan, that the special cash dividend was unusual and non-recurring and that appropriate adjustment to the stock options to purchase shares of the Company’s common stock outstanding under the 2011 Plan was required. The Company treated this adjustment as a modification to the original stock option grant because the terms of the agreements were modified in order to preserve the value of the option awards after a large non-recurring cash dividend. T hese options were amended to decrease the exercise price and increase the shares subject to the stock option. However, as the fair value of the underlying stock decreased more than the exercise price upon modification, and the result was a decrease in the fair value of such options. Accordingly, no incremental value was provided and no additional compensation cost was recorded by the Company. At September 30, 2019, there were 1.2 million shares remaining available for grant under the 2011 Plan. The weighted-average grant date fair value per share of stock options granted during the three and nine months ended September 30, 2019 was $3.53. The weighted-average grant date fair value per share of stock options granted during the nine months ended September 30, 2018. The fair value of stock options granted to employees during the nine months ended September 30, 2019 and 2018 was estimated at the date of grant using the following assumptions: Nine Months Ended September 30, 2019 2018 Risk-free interest rate 1.8 % 2.3 – 2.9% Expected dividend yield 0 % 0% Expected term 5.4 years 5.3 - 5.8 years Expected volatility 67 % 62 – 64% The Company recognized stock-based compensation expense during the three and nine months ended September 30, 2019 and 2018 as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2019 2018 2019 2018 Research and development expense $ — $ 256 $ 223 $ 870 General and administrative expense 703 526 1,561 1,456 Total stock-based compensation expense $ 703 $ 782 $ 1,784 $ 2,326

Net Loss Per Common Share

Net Loss Per Common Share	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Net Loss Per Common Share	9. 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 and nine months ended September 30, 2019 and 2018, as the Company was in a loss position and had no shares that met the definition of participating securities outstanding as of September 30, 2019 and 2018. Stock options are excluded from the calculation of diluted loss per share because the net loss for the three and nine months ended September 30, 2018 causes such securities to be anti-dilutive. Outstanding options excluded from the calculation of diluted loss per share for the three and nine months ended September 30, 2019 and 2018 are shown in the chart below: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2019 2018 2019 2018 Outstanding options to purchase common stock 1,781 1,806 1,781 1,806

Restructuring Activities

Restructuring Activities	9 Months Ended
	Sep. 30, 2019
Restructuring And Related Activities [Abstract]
Restructuring Activities	10. Restructuring Activities On November 7, 2018, the Company announced that it was implementing a reduction in headcount as part of a corporate restructuring. The corporate restructuring followed a comprehensive review of the Company’s product candidate pipeline. Under this corporate restructuring, the Company recognized total restructuring expenses of $1.3 million for the year ended December 31, 2018 consisting of one-time employee termination benefits of $1.0 million recorded in research and development expense and $0.3 million recorded in general and administrative expense. These one-time employee termination benefits are comprised of severance, benefits and related costs, all of which are expected to result in cash expenditures. Approximately $0.4 million of these payments were made during the fourth quarter of 2018, and the accrued remaining payments at December 31, 2018 were approximately $0.9 million. During the three months ended September 30, 2019, the Company reversed restructuring expenses of $0.1 million, consisting of one-time employee termination benefits of $0.1 million recorded in general and administrative expense. the Company recognized additional restructuring expenses of $4.8 million, consisting of one-time employee termination benefits of $2.0 million recorded in research and development expense and $2.8 million recorded in general and administrative expense. These one-time employee termination benefits are comprised of severance, benefits and related costs, all of which are expected to result in cash expenditures. During the three and nine months ended September 30, 2019, the Company paid approximately $0.8 million and $5.6 million of these restructuring expenses, respectively. As a result of the restructuring announced on January 8, 2017, the Company paid $0.2 million and $0.6 million, respectively, in restructuring expense for the three and nine months ended September 30, 2018. There were no restructuring expenses for the three and nine months ended September 30, 2018. As of July 12, 2019, the Company has no employees. The following table summarizes the charges related to the restructuring activities as of September 30, 2019: (in thousands) Accrued Restructuring Expenses at December 31, 2018 Expenses Less: Payments Accrued Restructuring Expenses at September 30, 2019 Severance, benefits and related costs due to workforce reduction $ 921 $ 4,825 $ (5,624 ) $ 122 Totals $ 921 $ 4,825 $ (5,624 ) $ 122

Investment in Silver Creek

Investment in Silver Creek	9 Months Ended
	Sep. 30, 2019
Noncontrolling Interest [Abstract]
Investment in Silver Creek	11. 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, the Company consolidated Silver Creek in its financial statements. Since the Company acquired its financial interest, Silver Creek has raised funding through the issuance of preferred stock and convertible promissory notes. 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 had the ability to exercise significant influence over Silver Creek. Under the equity method of accounting, the Company has recorded its proportionate share of Silver Creek’s losses in its results of operations with a corresponding decrease in the carrying value of the investment. As of May 7, 2019, the carrying value of the Company’s investment in Silver Creek was $6.4 million. On May 7, 2019, the Company sold its entire equity position in Silver Creek for $7.8 million. Accordingly, a $1.4 million of gain on sale of its equity investment was recognized during the nine months ended September 30, 2019 within other (expense) income, net in the condensed consolidated statement of operations and comprehensive loss.

14ner Sales Transaction

14ner Sales Transaction	9 Months Ended
	Sep. 30, 2019
Business Combinations [Abstract]
14 Ner Sales Transaction	12. 14ner Sales Transaction On July 12, 2019, the Company completed the 14ner Sale. In connection with the 14ner Sale, the Company received an upfront cash payment of $3.5 million and recognized in gain on sale of assets during the three and nine months ended September 30, 2019. The Company is also eligible to receive up to $54.5 million in additional potential development, regulatory approval and commercial-based milestone payments, consisting of: • $3.0 million for achievement of the primary endpoint in the first registrational clinical study of either MM-121 or MM-111; • Up to $16.5 million in total payments for the achievement of various regulatory approval and reimbursement-based milestones in the United States, Europe and Japan; and • Up to $35.0 million in total payments for achieving various cumulative worldwide net sales targets between $100.0 million and $300.0 million for MM-121 and MM-111.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2019
Accounting Changes And Error Corrections [Abstract]
Recent Accounting Pronouncements	13. Recent Accounting Pronouncements In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, “Leases (Topic 842)” (“ASU 2016-02”), which establishes principles that lessees and lessors shall apply to report useful information to users of financial statements about the amount, timing and uncertainty of cash flows arising from a lease. The most notable change will be lessees recognizing an asset and liability on their balance sheet for operating leases. In 2018, the FASB issued ASU 2018-01 and ASU 2018-11, which collectively add two practical expedients, provide a second modified retrospective transition method which does not require retrospective adjustment of prior periods, and provide certain narrow scope improvements to the new lease guidance. ASU 2016-02 and the amending ASU’s are effective for the Company for annual periods beginning after December 15, 2018 and interim periods therein, with early adoption permitted. The Company adopted the new guidance as of January 1, 2019 using the modified retrospective transition method, which does not require restatement of prior periods, for all leases existing as of the adoption date. As described in Note 3, “Leases,” the adoption of this new guidance did not have a material impact on the Company’s condensed consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, “Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In August 2018, the FASB issued ASU No. 2018-13, “Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement” (“ASU 2018-13”). This standard eliminates, adds and modifies certain disclosure requirements for fair value measurements as part of its disclosure framework project. ASU 2018-13 is effective for annual reporting periods beginning after December 15, 2019 and interim periods within those annual periods and early adoption is permitted. The Company is currently evaluating the impact that the adoption of this guidance may have on its 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.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2019
Subsequent Events [Abstract]
Subsequent Events	14. Subsequent Events In accordance with ASC 855-10 the Company has analyzed its operations subsequent to September 30, 2019 to the date these financial statements were issued, and has determined that it does not have any material subsequent events to disclose in these financial statements.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
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 subsidiaries. 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, 2018.
Consolidation	Consolidation The accompanying condensed consolidated financial statements reflect Merrimack Pharmaceuticals, Inc. and its wholly owned subsidiaries.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The condensed consolidated balance sheet as of December 31, 2018 was derived from audited financial statements, but does not include all disclosures required by GAAP. The condensed consolidated balance sheet as of September 30, 2019, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2019 and 2018, the condensed consolidated statements of stockholders’ equity for the three and nine months ended September 30, 2019 and 2018 and the condensed consolidated statements of cash flows for the nine months ended September 30, 2019 and 2018 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 September 30, 2019, the results of its operations for the three and nine months ended September 30, 2019 and 2018, its statements of stockholders’ equity for the three and nine months ended September 30, 2019 and 2018 and its statements of cash flows for the nine months ended September 30, 2019 and 2018. The financial data and other information disclosed in the notes related to the three and nine months ended September 30, 2019 and 2018 are unaudited. The results for the three and nine months ended September 30, 2019 and 2018 are not necessarily indicative of results to be expected for the year ending December 31, 2019, 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, 2018 filed with the SEC on March 6, 2019.
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) September 30, 2019 September 30, 2018 Cash and cash equivalents $ 20,858 $ 49,794 Restricted cash (long-term) — 584 Total cash, cash equivalents and restricted cash shown in the condensed consolidated statement of cash flows $ 20,858 $ 50,378 Restricted cash on the statement of financial position for 2018 primarily represents amounts pledged as collateral for operating lease obligations as contractually required.
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 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.
Recent Accounting Pronouncements	In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2016-02, “Leases (Topic 842)” (“ASU 2016-02”), which establishes principles that lessees and lessors shall apply to report useful information to users of financial statements about the amount, timing and uncertainty of cash flows arising from a lease. The most notable change will be lessees recognizing an asset and liability on their balance sheet for operating leases. In 2018, the FASB issued ASU 2018-01 and ASU 2018-11, which collectively add two practical expedients, provide a second modified retrospective transition method which does not require retrospective adjustment of prior periods, and provide certain narrow scope improvements to the new lease guidance. ASU 2016-02 and the amending ASU’s are effective for the Company for annual periods beginning after December 15, 2018 and interim periods therein, with early adoption permitted. The Company adopted the new guidance as of January 1, 2019 using the modified retrospective transition method, which does not require restatement of prior periods, for all leases existing as of the adoption date. As described in Note 3, “Leases,” the adoption of this new guidance did not have a material impact on the Company’s condensed consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, “Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In August 2018, the FASB issued ASU No. 2018-13, “Disclosure Framework – Changes to the Disclosure Requirements for Fair Value Measurement” (“ASU 2018-13”). This standard eliminates, adds and modifies certain disclosure requirements for fair value measurements as part of its disclosure framework project. ASU 2018-13 is effective for annual reporting periods beginning after December 15, 2019 and interim periods within those annual periods and early adoption is permitted. The Company is currently evaluating the impact that the adoption of this guidance may have on its 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 Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2019
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) September 30, 2019 September 30, 2018 Cash and cash equivalents $ 20,858 $ 49,794 Restricted cash (long-term) — 584 Total cash, cash equivalents and restricted cash shown in the condensed consolidated statement of cash flows $ 20,858 $ 50,378

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2019
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 September 30, 2019 and December 31, 2018: September 30, 2019 (in thousands) Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 16,705 $ — $ — Totals $ 16,705 $ — $ — December 31, 2018 (in thousands) Level 1 Level 2 Level 3 Cash equivalents: Money market funds $ 16,292 $ — $ — Commercial paper — 1,998 — Totals $ 16,292 $ 1,998 $ — Marketable securities: Commercial paper $ — $ 31,766 $ — Corporate debt securities — 7,479 — Government securities — 11,954 — Totals $ — $ 51,199 $ —

Marketable Securities and Cas_2

Marketable Securities and Cash Equivalents (Tables)	9 Months Ended
	Sep. 30, 2019
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 September 30, 2019 and December 31, 2018: September 30, 2019 (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds $ 16,705 $ — $ — $ 16,705 Total cash equivalents $ 16,705 $ — $ — $ 16,705 December 31, 2018 (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Cash equivalents: Money market funds $ 16,292 $ — $ — $ 16,292 Commercial paper 1,998 — — 1,998 Total cash equivalents $ 18,290 $ — $ — $ 18,290 Marketable securities: Commercial paper $ 31,766 $ — $ — $ 31,766 Corporate debt securities 7,487 — (8 ) 7,479 Government securities 11,955 — (1 ) 11,954 Total marketable securities $ 51,208 $ — $ (9 ) $ 51,199

Accounts Payable, Accrued Exp_2

Accounts Payable, Accrued Expenses and Other (Tables)	9 Months Ended
	Sep. 30, 2019
Payables And Accruals [Abstract]
Schedule of Accounts Payable, Accrued Expenses and Other	Accounts payable, accrued expenses and other as of September 30, 2019 and December 31, 2018 consisted of the following: (in thousands) September 30, 2019 December 31, 2018 Accounts payable $ 710 $ 1,034 Accrued goods and services 1,399 2,082 Accrued clinical trial costs 684 1,683 Accrued drug purchase costs 371 4,245 Accrued payroll and related benefits — 2,315 Accrued restructuring expenses 122 921 Income taxes payable 83 83 Deferred tax incentives 1,314 1,314 Total accounts payable, accrued expenses and other $ 4,683 $ 13,677

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2019
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 nine months ended September 30, 2019 and 2018 was estimated at the date of grant using the following assumptions: Nine Months Ended September 30, 2019 2018 Risk-free interest rate 1.8 % 2.3 – 2.9% Expected dividend yield 0 % 0% Expected term 5.4 years 5.3 - 5.8 years Expected volatility 67 % 62 – 64%
Schedule of Recognized Stock-Based Compensation Expense	The Company recognized stock-based compensation expense during the three and nine months ended September 30, 2019 and 2018 as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2019 2018 2019 2018 Research and development expense $ — $ 256 $ 223 $ 870 General and administrative expense 703 526 1,561 1,456 Total stock-based compensation expense $ 703 $ 782 $ 1,784 $ 2,326

Net Loss Per Common Share (Tabl

Net Loss Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Schedule of Outstanding Options Excluded from Computation of Diluted Loss Per Share	Outstanding options excluded from the calculation of diluted loss per share for the three and nine months ended September 30, 2019 and 2018 are shown in the chart below: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2019 2018 2019 2018 Outstanding options to purchase common stock 1,781 1,806 1,781 1,806

Restructuring Activities (Table

Restructuring Activities (Tables)	9 Months Ended
	Sep. 30, 2019
Restructuring And Related Activities [Abstract]
Summary of Charges Related to Restructuring Activities	The following table summarizes the charges related to the restructuring activities as of September 30, 2019: (in thousands) Accrued Restructuring Expenses at December 31, 2018 Expenses Less: Payments Accrued Restructuring Expenses at September 30, 2019 Severance, benefits and related costs due to workforce reduction $ 921 $ 4,825 $ (5,624 ) $ 122 Totals $ 921 $ 4,825 $ (5,624 ) $ 122

Nature of the Business - Additi

Nature of the Business - Additional Information (Detail) - USD ($)

Dec. 31, 2019

Jul. 12, 2019

May 07, 2019

Apr. 03, 2017

May 31, 2019

Sep. 30, 2019

Jun. 30, 2019

Mar. 31, 2019

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Sep. 30, 2019

Sep. 30, 2018

Apr. 15, 2019

Dec. 31, 2018

Apr. 30, 2017

Summary Of Significant Accounting Policies [Line Items]

Proceeds from sale of equity securities

$ 51,500,000

$ 42,200,000

Proceeds from sale of research and development operations

2,025,000

Special cash dividend paid

$ 20,000,000

$ 20,000,000

Dividend payable date

Sep. 5, 2019

Sep. 5, 2019

Dividend payable, date of record

Aug. 28, 2019

Aug. 28, 2019

Accumulated deficit

$ 543,870,000

$ 543,870,000

$ 523,277,000

Net loss

$ 705,000

705,000

$ 9,430,000

$ 10,458,000

$ (3,989,000)

$ 17,769,000

$ 17,782,000

20,593,000

31,562,000

Cash used in operating activities

28,728,000

46,696,000

Cash and cash equivalents

$ 20,858,000

$ 49,794,000

$ 20,858,000

$ 49,794,000

$ 20,079,000

Silver Creek Pharmaceuticals, Inc. [Member]

Summary Of Significant Accounting Policies [Line Items]

Proceeds from sale of equity securities

$ 7,800,000

$ 7,800,000

Silver Creek Pharmaceuticals, Inc. [Member] | Laboratory Equipment [Member]

Summary Of Significant Accounting Policies [Line Items]

Proceeds from sale of research and development operations

$ 1,400,000

Loan Agreement [Member] | Hercules Capital, Inc [Member] | Term Loan [Member]

Summary Of Significant Accounting Policies [Line Items]

Payoff amount

$ 16,000,000

Ipsen [Member] | Ongoing Multi Part Clinical [Member]

Summary Of Significant Accounting Policies [Line Items]

Contingent milestone payments receivable

$ 5,000,000

Ipsen [Member] | First Line Treatment of Metastatic Adenocarcinoma of Pancreas [Member]

Summary Of Significant Accounting Policies [Line Items]

Contingent milestone payments receivable

225,000,000

Ipsen [Member] | After Failure of First Line Chemotherapy [Member]

Summary Of Significant Accounting Policies [Line Items]

Contingent milestone payments receivable

150,000,000

Ipsen [Member] | Additional Indication [Member]

Summary Of Significant Accounting Policies [Line Items]

Contingent milestone payments receivable

75,000,000

Ipsen [Member] | Asset Sale Agreement [Member] | Maximum [Member]

Summary Of Significant Accounting Policies [Line Items]

Contingent milestone payments receivable

$ 455,000,000

Additional payments receivable on achievement of certain milestone events

450,000,000

Servier [Member] | Asset Sale Agreement [Member] | Development and Commercialization Milestones [Member]

Summary Of Significant Accounting Policies [Line Items]

Remaining milestone payments received

5,000,000

Milestone payment received

28,000,000

Maximum amount of milestone payments that can be received

$ 33,000,000

14ner Sale [Member]

Summary Of Significant Accounting Policies [Line Items]

Upfront cash payment received

$ 3,500,000

14ner Sale [Member] | Maximum [Member]

Summary Of Significant Accounting Policies [Line Items]

Additional payments receivable on achievement of certain milestone events

54,500,000

14ner Sale [Member] | Maximum [Member] | Achievement of the Primary Endpoint in the First Registrational Clinical Study of Either MM-121 or MM-111 [Member]

Summary Of Significant Accounting Policies [Line Items]

Additional payments receivable on achievement of certain milestone events

3,000,000

14ner Sale [Member] | Maximum [Member] | Achievement of Various Regulatory Approval and Reimbursement-Based Milestones in the United States, Europe and Japan [Member]

Summary Of Significant Accounting Policies [Line Items]

Additional payments receivable on achievement of certain milestone events

16,500,000

14ner Sale [Member] | Maximum [Member] | Achievement Various Cumulative Worldwide Net Sales Targets Between $100.0 million and $300.0 million for MM-121 and MM-111 [Member]

Summary Of Significant Accounting Policies [Line Items]

Additional payments receivable on achievement of certain milestone events

35,000,000

Cumulative worldwide net sales target

300,000,000

14ner Sale [Member] | Minimum [Member] | Achievement Various Cumulative Worldwide Net Sales Targets Between $100.0 million and $300.0 million for MM-121 and MM-111 [Member]

Summary Of Significant Accounting Policies [Line Items]

Cumulative worldwide net sales target

$ 100,000,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 20,858	$ 20,079	$ 49,794
Restricted cash (long-term)			584
Total cash, cash equivalents and restricted cash shown in the condensed consolidated statement of cash flows	$ 20,858	$ 20,663	$ 50,378	$ 94,217

Leases - Additional Information

Leases - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2019
One Kendall Square in Cambridge, Massachusetts [Member]
Lessee Lease Description [Line Items]
Operating lease expiration month and year	2019-06

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Summary of Assets Measured at Fair Value on a Recurring Basis (Detail) - Recurring Basis [Member] - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	$ 16,705	$ 16,292
Level 1 [Member] | Money Market Funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	$ 16,705	16,292
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		1,998
Marketable securities		51,199
Level 2 [Member] | Commercial Paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		1,998
Marketable securities		31,766
Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities		7,479
Level 2 [Member] | US Treasury And Government [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities		$ 11,954

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Additional Information (Detail) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair value transfers between Level 1 and Level 2	$ 0	$ 0

Marketable Securities and Cas_3

Marketable Securities and Cash Equivalents - Summary of Marketable Securities and Cash Equivalents (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Marketable Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		$ 51,208
Unrealized Losses		(9)
Fair Value		51,199
Corporate Debt Securities [Member] | Marketable Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		7,487
Unrealized Losses		(8)
Fair Value		7,479
Commercial Paper [Member] | Marketable Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		31,766
Fair Value		31,766
Government Securities [Member] | Marketable Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		11,955
Unrealized Losses		(1)
Fair Value		11,954
Cash Equivalents [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 16,705	18,290
Fair Value	16,705	18,290
Cash Equivalents [Member] | Money Market Funds [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	16,705	16,292
Fair Value	$ 16,705	16,292
Cash Equivalents [Member] | Commercial Paper [Member]
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost		1,998
Fair Value		$ 1,998

Notes Payable - Additional Info

Notes Payable - Additional Information (Detail) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Apr. 15, 2019
Debt Instrument [Line Items]
Loss on extinguishment of debt				$ 971,000
Interest expense			$ 472,000	1,527,000	$ 472,000
Loan Agreement [Member]
Debt Instrument [Line Items]
Interest expense	$ 0		$ 0	$ 1,500,000	$ 0
Term Loan [Member] | Loan Agreement [Member] | Hercules Capital, Inc [Member]
Debt Instrument [Line Items]
Aggregate principal amount of loan						$ 15,000,000
Debt discount discount and issuance costs						400,000
Payments of fee						300,000
Payoff amount						16,000,000
Prepayment penalty						200,000
Prepayment fee						$ 800,000
Loss on extinguishment of debt		$ 1,000,000

Accounts Payable, Accrued Exp_3

Accounts Payable, Accrued Expenses and Other - Schedule of Accounts Payable, Accrued Expenses and Other (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accounts payable	$ 710	$ 1,034
Accrued goods and services	1,399	2,082
Accrued clinical trial costs	684	1,683
Accrued drug purchase costs	371	4,245
Accrued payroll and related benefits		2,315
Accrued restructuring expenses	122	921
Income taxes payable	83	83
Deferred tax incentives	1,314	1,314
Total accounts payable, accrued expenses and other	$ 4,683	$ 13,677

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions	Jul. 12, 2019	Sep. 30, 2019	Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Special cash dividend paid	$ 20,000,000		$ 20,000,000
Dividend payable date	Sep. 5, 2019		Sep. 5, 2019
Dividend payable, date of record	Aug. 28, 2019		Aug. 28, 2019
Incremental compensation expense			$ 0
Additional compensation expense			$ 0
Weighted-average grant date fair value per share of stock options		$ 3.53	$ 3.53
Stock Incentive Plan 2011 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock available for grant		1.2	1.2

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]	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	1.80%
Expected volatility	67.00%
Expected dividend yield	0.00%	0.00%
Expected term	5 years 4 months 24 days
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate		2.30%
Expected volatility		62.00%
Expected term		5 years 3 months 19 days
Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate		2.90%
Expected volatility		64.00%
Expected term		5 years 9 months 18 days

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Recognized Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 703	$ 782	$ 1,784	$ 2,326
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		256	223	870
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	$ 703	$ 526	$ 1,561	$ 1,456

Net Loss Per Common Share - Add

Net Loss Per Common Share - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Amounts allocated to participating securities	$ 0	$ 0	$ 0	$ 0
Participating securities outstanding, shares	0	0	0	0

Net Loss Per Common Share - Sch

Net Loss Per Common Share - Schedule of Outstanding Options Excluded from Computation of Diluted Loss Per Share (Detail) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Outstanding Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Securities excluded from calculation of diluted loss per share	1,781	1,806	1,781	1,806

Restructuring Activities- Addit

Restructuring Activities- Additional Information (Detail) $ in Thousands	Jul. 12, 2019Employee	Sep. 30, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)
Restructuring Cost And Reserve [Line Items]
Restructuring expenses				$ 0	$ 4,825	$ 0
Payments for restructuring		$ 800	$ 400	$ 200	5,624	$ 600	$ 900
Number of employees | Employee	0
One-time Termination Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses		100			4,800		1,300
One-time Termination Benefits [Member] | Research and Development Expense [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses					2,000		1,000
One-time Termination Benefits [Member] | General and Administrative Expense [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring expenses		$ 100			$ 2,800		$ 300
November 2018 Corporate Restructuring [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring activity, announcement date					Nov. 7, 2018

Restructuring Activities - Summ

Restructuring Activities - Summary of Charges Related to Restructuring Activities (Detail) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Restructuring Cost And Reserve [Line Items]
Accrued Restructuring Expenses				$ 921
Expenses			$ 0	4,825	$ 0
Less: Payments	$ (800)	$ (400)	$ (200)	(5,624)	$ (600)	$ (900)
Accrued Restructuring Expenses	122	921		122		921
Severance Benefits and Related Costs Due to Workforce Reduction [Member]
Restructuring Cost And Reserve [Line Items]
Accrued Restructuring Expenses				921
Expenses				4,825
Less: Payments				(5,624)
Accrued Restructuring Expenses	$ 122	$ 921		$ 122		$ 921

Investment in Silver Creek - Ad

Investment in Silver Creek - Additional Information (Detail) - USD ($) $ in Thousands	May 07, 2019	May 31, 2019	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Sep. 30, 2017
Consolidation Less Than Wholly Owned Subsidiary Parent Ownership Interest Effects Of Changes Net [Line Items]
Equity method investment					$ 7,428
Proceeds from maturities and sales of marketable securities			$ 51,500	$ 42,200
Equity method investment realized gain loss on sale			$ 1,400
Silver Creek Pharmaceuticals, Inc. [Member]
Consolidation Less Than Wholly Owned Subsidiary Parent Ownership Interest Effects Of Changes Net [Line Items]
Equity method investment	$ 6,400
Proceeds from maturities and sales of marketable securities	$ 7,800	$ 7,800
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%

14ner Sales Transaction - Addit

14ner Sales Transaction - Additional Information (Detail) - 14ner Sale [Member]	Jul. 12, 2019USD ($)
Business Acquisition [Line Items]
Upfront cash payment received	$ 3,500,000
Maximum [Member]
Business Acquisition [Line Items]
Additional payments receivable on achievement of certain milestone events	54,500,000
Maximum [Member] | Achievement of the Primary Endpoint in the First Registrational Clinical Study of Either MM-121 or MM-111 [Member]
Business Acquisition [Line Items]
Additional payments receivable on achievement of certain milestone events	3,000,000
Maximum [Member] | Achievement of Various Regulatory Approval and Reimbursement-Based Milestones in the United States, Europe and Japan [Member]
Business Acquisition [Line Items]
Additional payments receivable on achievement of certain milestone events	16,500,000
Maximum [Member] | Achievement Various Cumulative Worldwide Net Sales Targets Between $100.0 million and $300.0 million for MM-121 and MM-111 [Member]
Business Acquisition [Line Items]
Additional payments receivable on achievement of certain milestone events	35,000,000
Cumulative worldwide net sales target	300,000,000
Minimum [Member] | Achievement Various Cumulative Worldwide Net Sales Targets Between $100.0 million and $300.0 million for MM-121 and MM-111 [Member]
Business Acquisition [Line Items]
Cumulative worldwide net sales target	$ 100,000,000