Basis of Presentation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Basis of Presentation
Cash, cash equivalents and marketable securities	$ 220,100		$ 220,100
Net Loss	$ (31,952)	$ (32,359)	(66,625)	$ (62,533)
Net cash used in operations			$ (68,732)	$ (57,351)