Basis of Presentation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Basis of Presentation
Cash, cash equivalents and marketable securities	$ 304,600		$ 304,600
Net Loss	$ (31,980)	$ (28,082)	(94,513)	$ (86,258)
Net cash used in operations			$ (85,142)	$ (79,323)