Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating expenses:
Research and development expenses	$ 12,959	$ 13,598	$ 39,743	$ 54,954
General and administrative expenses	3,777	3,366	11,560	23,798
Total operating expenses	16,736	16,964	51,303	78,752
Loss from continuing operations	(16,736)	(16,964)	(51,303)	(78,752)
Other income and expenses:
Interest income	306	250	863	646
Interest expense	(472)	(1,659)	(472)	(30,400)
Gain on deconsolidation of Silver Creek Pharmaceuticals, Inc.		10,848		10,848
Gain on sale of asset				1,703
Other income (expense), net	(237)	69	(1,778)	(592)
Total other income and expenses	(403)	9,508	(1,387)	(17,795)
Net loss from continuing operations before income tax benefit	(17,139)	(7,456)	(52,690)	(96,547)
Income tax benefit	4,798	2,133	4,798	32,372
Net loss from continuing operations	(12,341)	(5,323)	(47,892)	(64,175)
Discontinued operations:
Income from discontinued operations, net of tax	16,330	8,456	16,330	547,994
Net income (loss)	3,989	3,133	(31,562)	483,819
Net income (loss) attributable to non-controlling interest		31		(1,160)
Net income (loss) attributable to Merrimack Pharmaceuticals, Inc.	3,989	3,102	(31,562)	484,979
Other comprehensive income (loss):
Unrealized loss on marketable securities	(4)		(5)
Other comprehensive income (loss)	(4)		(5)
Comprehensive income (loss)	3,985	3,102	(31,567)	484,979
Amounts attributable to Merrimack Pharmaceuticals, Inc.:
Net loss from continuing operations	(12,341)	(5,354)	(47,892)	(63,015)
Income from discontinued operations, net of tax	16,330	8,456	16,330	547,994
Net income (loss) attributable to Merrimack Pharmaceuticals, Inc.	$ 3,989	$ 3,102	$ (31,562)	$ 484,979
Basic and dilutive net income (loss) per common share
Net loss from continuing operations	$ (0.92)	$ (0.40)	$ (3.59)	$ (4.77)
Net income from discontinued operations, net of tax	1.22	0.64	1.22	41.52
Net income (loss) per share	$ 0.30	$ 0.24	$ (2.37)	$ 36.75
Weighted-average common shares used per share calculations—basic and diluted	13,343	13,282	13,343	13,197
Cash dividend paid per common share				$ 10.55