Net Loss Per Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net loss	$ (6,289)	$ (30,044)	$ (87,823)	$ (108,278)
Denominator:
Weighted-average number of common shares used in loss per share - basic and diluted (in shares)	46,493,126	46,141,217	46,395,124	45,975,691
Loss per share - basic and diluted (in dollars per share)	$ (0.14)	$ (0.65)	$ (1.89)	$ (2.36)