Net Loss per Share - Calculation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net loss	$ (100,734)	$ (38,875)	$ (208,509)	$ (95,414)
Weighted average common shares used for basic and diluted net loss per share computation (in shares)	89,158	86,714	88,814	86,374
Net loss per common share:
Basic and Diluted (in usd per share)	$ (1.13)	$ (0.45)	$ (2.35)	$ (1.10)