Consolidated Statements of Operations and Comprehensive Loss - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues:
Product revenues, net	$ 4,328	$ 0	$ 0
License and collaboration revenues	84,930	102,756	47,786
Total revenues	89,258	102,756	47,786
Costs and expenses:
Cost of product revenues	46	0	0
Research and development expenses	160,988	138,495	147,139
Selling, general and administrative expenses	57,795	30,517	21,187
Total costs and expenses	218,829	169,012	168,326
Loss from operations	(129,571)	(66,256)	(120,540)
Other income and expenses
Interest income	99	114	166
Interest expense	(19,232)	(18,230)	(10,938)
Other income, net	917	813	627
Net loss	(147,787)	(83,559)	(130,685)
Less net income (loss) attributable to non-controlling interest	170	(268)	240
Net loss attributable to Merrimack Pharmaceuticals, Inc.	(147,957)	(83,291)	(130,925)
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities	74	(50)	14
Other comprehensive income (loss)	74	(50)	14
Comprehensive loss	$ (147,883)	$ (83,341)	$ (130,911)
Net loss per share available to common stockholders-basic and diluted	$ (1.33)	$ (0.80)	$ (1.32)
Weighted-average common shares used in computing net loss per share available to common stockholders-basic and diluted	111,356	104,410	98,919