Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Collaboration revenue	$ 19,024	$ 18,123	$ 1,293
Operating expenses:
Research and development	12,875	38,254	68,468
General and administrative	14,217	18,589	28,712
Restructuring and lease exit	4,358	11,729	8,017
Operating Expenses, Total	31,450	68,572	105,197
Loss from operations	(12,426)	(50,449)	(103,904)
Other income and expense:
Other (expense) income, net	(289)	66	(123)
Interest expense	(2,307)	(2,388)	(3,127)
Interest income	21	32	125
Other expense, net	(2,575)	(2,290)	(3,125)
Net loss	$ (15,001)	$ (52,739)	$ (107,029)
Basic and diluted net loss per share:
Net loss per share	$ (0.27)	$ (1.01)	$ (2.10)
Weighted average number of common shares outstanding	55,701	52,289	50,928