Statements of Operations (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		118 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013
Research contract revenue	$ 200	$ 200	$ 400	$ 400	$ 1,867
Operating expenses:
Research and development, including costs of research contracts	14,775	18,264	33,887	32,249	246,232
General and administrative	3,721	4,902	8,392	9,750	96,710
Total operating expenses	18,496	23,166	42,279	41,999	342,942
Loss from operations	(18,296)	(22,966)	(41,879)	(41,599)	(341,075)
Other income (expense), net	7	3	3	(23)	4,704
Change in fair value of warrants	(403)	(650)	10,385	(6,461)	21,156
Net loss	$ (18,692)	$ (23,613)	$ (31,491)	$ (48,083)	$ (315,215)
Net loss per share - basic and diluted	$ (0.22)	$ (0.30)	$ (0.38)	$ (0.62)
Weighted average common shares outstanding to compute net loss per share - basic and diluted	83,082,633	78,514,718	82,994,845	77,067,424