Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Revenues:
Product revenues, net	$ 12,851		$ 22,819
License and collaboration revenues	19,332	$ 36,558	30,645	$ 51,399
Other revenues	1,498		1,498
Total revenues	33,681	36,558	54,962	51,399
Costs and expenses:
Cost of revenues	1,872		2,583
Research and development expenses	40,996	42,806	73,878	78,485
Selling, general and administrative expenses	20,680	12,315	38,475	21,504
Total costs and expenses	63,548	55,121	114,936	99,989
Loss from operations	(29,867)	(18,563)	(59,974)	(48,590)
Other income and expenses:
Interest income	122	34	194	80
Interest expense	(21,149)	(4,482)	(29,729)	(9,048)
Other (expense) income, net	(64)	110	(107)	224
Net loss	(50,958)	(22,901)	(89,616)	(57,334)
Net (loss) income attributable to non-controlling interest	(208)	(123)	(393)	204
Net loss attributable to Merrimack Pharmaceuticals, Inc.	(50,750)	(22,778)	(89,223)	(57,538)
Other comprehensive income:
Unrealized gain on available-for-sale securities	15	21	1	68
Other comprehensive income	15	21	1	68
Comprehensive loss	$ (50,735)	$ (22,757)	$ (89,222)	$ (57,470)
Net loss per share available to common stockholders—basic and diluted	$ (0.40)	$ (0.21)	$ (0.74)	$ (0.53)
Weighted-average common shares used in computing net loss per share available to common stockholders—basic and diluted	126,161	109,975	121,112	108,662