Net Loss Per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net loss	$ (154,740)	$ (24,010)	$ (76,350)
Denominator:
Weighted-average shares outstanding - basic and diluted	107,900	100,244	98,539
Net loss per common share - basic and diluted:	$ (1.43)	$ (0.24)	$ (0.77)