Consolidated Statements of Operations and Comprehensive Loss (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended		38 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012
Consolidated Statements of Operations and Comprehensive Loss [Abstract]
Revenues
Operating Expenses:
Research and development	12,590	9,679	25,152	16,720	89,963
General and administrative	2,680	1,705	5,105	3,110	18,476
Acquired in-process research and development	250	7,000	4,250	7,000	36,335
Operating loss	(15,520)	(18,384)	(34,507)	(26,830)	(144,774)
Other income (expense), net	(172)	(115)	(176)	3	(381)
Loss before income taxes	(15,692)	(18,499)	(34,683)	(26,827)	(145,155)
Income taxes	35		27
Net loss	(15,657)	(18,499)	(34,656)	(26,827)	(145,155)
Basic and diluted net loss per common share	$ (0.61)	$ (14.32)	$ (1.45)	$ (21.07)	$ (26.14)
Basic and diluted weighted average common shares outstanding	25,744	1,292	23,892	1,273	5,552
Comprehensive loss	$ (15,661)	$ (18,514)	$ (34,658)	$ (26,848)	$ (145,108)