Basis of Presentation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Basis of Presentation
Cash, cash equivalents and marketable securities	$ 334,000		$ 334,000
Net Loss	$ (32,359)	$ (28,274)	(62,533)	$ (58,177)
Net cash used in operations			$ (57,351)	$ (52,731)