Consolidated Statements of Operations (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended			131 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012
Revenue:
Research revenue	$ 11,591	$ 14,794		$ 57,493
Collaboration and milestone revenue	6,820	6,640	922	64,382
Total revenue	18,411	21,434	922	121,875
Operating Expenses:
Research and development	50,273	50,856	39,042	315,893
General and administrative	19,364	19,880	15,660	132,613
Restructuring charges				1,522
Impairment of leasehold improvements				1,030
Depreciation and amortization	1,705	1,585	2,058	11,768
In-process research and development				418
Total operating expenses	71,342	72,321	56,760	463,244
Loss from operations	(52,931)	(50,887)	(55,838)	(341,369)
Other income (expenses):
Interest income	316	160	156	14,389
Interest expense	(89)	(148)	(260)	(2,422)
Change in fair value of warrant liability	653	2,764	(1,410)	1,553
Other income	21	70	1,277	252
Loss before income tax benefit	(52,030)	(48,041)	(56,075)	(327,597)
Income tax benefit	3,245	3,629	1,139	8,708
Net loss	(48,785)	(44,412)	(54,936)	(318,889)
Deemed dividend				(19,424)
Preferred stock accretion				(802)
Net loss attributable to common stockholders	$ (48,785)	$ (44,412)	$ (54,936)	$ (339,115)
Net loss attributable to common stockholders per common share - basic and diluted (in dollars per share)	$ (1.07)	$ (1.28)	$ (1.98)
Weighted-average common shares outstanding - basic and diluted (in shares)	45,565,217	34,569,642	27,734,797