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	1,673		1,673
Exercise of employee stock options (in shares)	455,168	455,168
Exercise of employee stock options	854	1	853
Exercise of warrants to purchase common stock (in shares)		49,315
Exercise of warrants to purchase common stock	101		172	(71)
Expired warrants			3,110	(3,110)
Cancelled restricted stock		(140,600)
Repurchase of shares of restricted common stock (in shares)		(60,041)
Repurchase of shares of restricted common stock	(250)		(250)
Net loss	(31,491)				(31,491)
Ending Balance at Jun. 30, 2013	$ 19,332	$ 84	$ 330,735	$ 3,728	$ (315,215)
Ending Balance (in shares) at Jun. 30, 2013		83,540,682