Basis of Presentation (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Basis of Presentation
Cash, cash equivalents and marketable securities	$ 182,400,000
Working capital	166,100,000
Term Loan	10,100,000
Net Loss	(17,332,000)	(13,516,000)
Net cash used in operations	$ (17,200,000)	$ (13,553,000)