Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Collaboration and licensing revenue	$ 2,515	$ 19,024	$ 18,123
Operating expenses:
Research and development	23,703	12,875	38,254
General and administrative	8,205	14,217	18,589
Restructuring and lease exit		4,358	11,729
Operating Expenses, Total	31,908	31,450	68,572
Loss from operations	(29,393)	(12,426)	(50,449)
Other income (expense), net:
Interest expense, net	(1,949)	(2,286)	(2,356)
Change in fair value of warrant liability	4,751
Other (expense) income	(195)	(289)	66
Other income (expense), net	2,607	(2,575)	(2,290)
Net loss before provision for income taxes	(26,786)	(15,001)	(52,739)
Provision for income taxes	(101)
Net loss	$ (26,887)	$ (15,001)	$ (52,739)
Basic and diluted net loss per share:
Net loss per share	$ (0.39)	$ (0.27)	$ (1.01)
Weighted average number of common shares outstanding	69,268	55,701	52,289