Basis of Presentation (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Basis of Presentation
Cash, cash equivalents and marketable securities	$ 78,700,000		$ 78,700,000
Working capital	67,800,000		67,800,000
Term loan	13,900,000		13,900,000
Net Loss	(13,773,000)	(10,236,000)	(27,289,000)	(20,295,000)
Net cash used in operations			(25,512,000)	(18,229,000)
Net proceeds from sale of common stock			$ 51,957,000	$ 35,889,000