Statements of Operations (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		121 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013
Research contract revenue	$ 200	$ 200	$ 600	$ 600	$ 2,067
Operating expenses:
Research and development, including costs of research contracts	6,247	16,215	40,133	48,464	252,478
General and administrative	3,068	5,712	11,459	15,462	99,777
Total operating expenses	9,315	21,927	51,592	63,926	352,255
Loss from operations	(9,115)	(21,727)	(50,992)	(63,326)	(350,188)
Other income (expense), net	(191)	(42)	(190)	(65)	4,511
Change in fair value of warrants	(7,407)	3,945	2,979	(2,516)	13,750
Net loss	$ (16,713)	$ (17,824)	$ (48,203)	$ (65,907)	$ (331,927)
Net loss per share-basic and diluted	$ (0.20)	$ (0.23)	$ (0.58)	$ (0.85)
Weighted average common shares outstanding to compute net loss per share-basic and diluted	83,161,927	78,670,222	83,051,151	77,605,590