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, 2020	Dec. 31, 2019	Dec. 31, 2018
Numerator:
Net loss	$ (91,581)	$ (73,859)	$ (154,740)
Denominator:
Weighted-average shares outstanding - basic and diluted	139,887	131,568	107,900
Net loss per common share - basic and diluted:	$ (0.65)	$ (0.56)	$ (1.43)