Net Loss Per Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net loss	$ (68,438)	$ (43,435)	$ (125,377)	$ (83,898)
Denominator:
Weighted-average number of common shares used in loss per share - basic and diluted (in shares)	43,410,053	43,042,883	43,300,243	43,027,903
Loss per share - basic and diluted (in dollars per share)	$ (1.58)	$ (1.01)	$ (2.90)	$ (1.95)