Condensed Consolidated Statements of Operations and Comprehensive Income (Loss) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Costs and expenses:
Research and development expenses	$ 19,751	$ 27,695	$ 41,356	$ 55,697
General and administrative expenses	14,798	8,138	20,432	14,590
Total costs and expenses	34,549	35,833	61,788	70,287
Loss from continuing operations	(34,549)	(35,833)	(61,788)	(70,287)
Other income and expenses:
Interest income	382	122	396	194
Interest expense	(26,762)	(15,858)	(28,741)	(19,148)
Gain on sale of asset	1,703		1,703
Other expense, net	(659)	(64)	(661)	(107)
Net loss from continuing operations before income tax benefit	(59,885)	(51,633)	(89,091)	(89,348)
Income tax benefit	30,239		30,239
Net loss from continuing operations	(29,646)	(51,633)	(58,852)	(89,348)
Discontinued operations:
Income (loss) from discontinued operations, net of tax	540,485	675	539,538	(268)
Net income (loss)	510,839	(50,958)	480,686	(89,616)
Net loss attributable to non-controlling interest	(724)	(208)	(1,191)	(393)
Net income (loss) attributable to Merrimack Pharmaceuticals, Inc.	511,563	(50,750)	481,877	(89,223)
Other comprehensive income (loss):
Unrealized gain on available-for-sale securities		15		1
Other comprehensive loss		15		1
Comprehensive income (loss)	511,563	(50,735)	481,877	(89,222)
Amounts attributable to Merrimack Pharmaceuticals, Inc.:
Net loss from continuing operations	(28,922)	(51,425)	(57,661)	(88,955)
Income (loss) from discontinued operations, net of tax	540,485	675	539,538	(268)
Net income (loss) attributable to Merrimack Pharmaceuticals, Inc.	$ 511,563	$ (50,750)	$ 481,877	$ (89,223)
Basic and dilutive net income (loss) per common share
Net loss from continuing operations	$ (0.22)	$ (0.41)	$ (0.44)	$ (0.74)
Net income (loss) from discontinued operations, net of tax	4.08	0.01	4.10	0.00
Net income (loss) per share	$ 3.86	$ (0.40)	$ 3.66	$ (0.74)
Weighted-average common shares used per share calculations—basic and diluted	132,457	126,161	131,528	121,112
Cash dividend paid per common share	$ 1.055		$ 1.055