Basis of Presentation (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Basis of Presentation
Cash, cash equivalents and marketable securities	$ 155,000,000		$ 155,000,000
Working capital	143,900,000		143,900,000
Net Loss	(19,016,000)	(13,773,000)	(36,348,000)	(27,289,000)
Net cash used in operations			$ (35,258,000)	$ (25,512,000)