Basis of Presentation (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Basis of Presentation
Cash, cash equivalents and marketable securities	$ 252,400,000		$ 252,400,000
Net Loss	(28,274,000)	(19,016,000)	(58,177,000)	(36,348,000)
Net cash used in operations			$ (52,731,000)	$ (35,258,000)