Basis of Presentation (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Basis of Presentation
Cash, cash equivalents and marketable securities	$ 77,600,000		$ 77,600,000
Working capital	63,700,000		63,700,000
Term loan	12,600,000		12,600,000
Net Loss	(15,027,000)	(11,772,000)	(42,316,000)	(32,067,000)
Net cash used in operations			(36,456,000)	(26,288,000)
Net proceeds from issuance of common stock			$ 62,872,000	$ 35,880,000