Basis of Presentation (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Basis of Presentation
Cash, cash equivalents and marketable securities	$ 224,100,000		$ 224,100,000
Net Loss	(28,082,000)	(23,140,000)	(86,258,000)	(59,488,000)
Net cash used in operations			$ (79,323,000)	$ (52,712,000)