Statement of Stockholders Equity (USD $) In Thousands, except Share data	Total	Common Stock	Additional Paid in Capital, Common Stock	Other Additional Capital	Accumulated Deficit during Development Stage
Beginning Balance at Dec. 31, 2012	$ 48,445	$ 83	$ 325,177	$ 6,909	$ (283,724)
Beginning Balance (in shares) at Dec. 31, 2012		83,236,840
Stock-based compensation	1,541		1,541
Exercise of employee stock options (in shares)	453,168	453,168
Exercise of employee stock options	851		851
Exercise of warrants to purchase common stock (in shares)		49,315
Exercise of warrants to purchase common stock	101	1	172	(72)
Cancelled restricted stock		(1,190)
Repurchase of shares of restricted common stock (in shares)		(57,284)
Repurchase of shares of restricted common stock	(246)		(246)
Net loss	(12,799)				(12,799)
Ending Balance at Mar. 31, 2013	$ 37,893	$ 84	$ 327,495	$ 6,837	$ (296,523)
Ending Balance (in shares) at Mar. 31, 2013		83,680,849