Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenues:
Product revenues, net	$ 14,493		$ 37,312
License and collaboration revenues	12,417	$ 16,440	43,062	$ 67,839
Other revenues	1,161		2,659
Total revenues	28,071	16,440	83,033	67,839
Costs and expenses:
Cost of revenues	1,010		3,593
Research and development expenses	32,078	37,763	105,956	116,248
Selling, general and administrative expenses	18,048	16,956	56,523	38,460
Restructuring expenses	809		809
Total costs and expenses	51,945	54,719	166,881	154,708
Loss from operations	(23,874)	(38,279)	(83,848)	(86,869)
Other income and expenses:
Interest income	64	13	258	93
Interest expense	(6,850)	(4,476)	(36,579)	(13,524)
Other income, net	385	356	278	580
Net loss	(30,275)	(42,386)	(119,891)	(99,720)
Net (loss) income attributable to non-controlling interest	(207)	208	(600)	412
Net loss attributable to Merrimack Pharmaceuticals, Inc.	(30,068)	(42,594)	(119,291)	(100,132)
Other comprehensive (loss) income:
Unrealized (loss) gain on available-for-sale securities	(3)	6	(2)	74
Other comprehensive (loss) income	(3)	6	(2)	74
Comprehensive loss	$ (30,071)	$ (42,588)	$ (119,293)	$ (100,058)
Net loss per share available to common stockholders—basic and diluted	$ (0.23)	$ (0.38)	$ (0.96)	$ (0.91)
Weighted-average common shares used in computing net loss per share available to common stockholders—basic and diluted	129,212	112,417	123,832	109,928