Basis of Presentation - (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Basis of Presentation
Cash, cash equivalents and marketable securities	$ 167,000
Net Loss	(34,261)	$ (34,673)
Net cash used in operations	$ 35,262	$ 34,902