Net Loss Per Share - Reconciliation of Numerator and Denominators in Computing Net Loss per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator:
Net loss	$ (58,004)	$ (58,896)	$ (55,630)	$ (60,089)	$ (53,324)	$ (25,800)	$ (172,530)	$ (139,213)
Denominator:
Shares used in basic net loss per share calculation (in shares)	55,905			55,548			55,831	53,039
Shares used in diluted net loss per share calculation (in shares)	55,905			55,548			55,831	53,039
Net loss per share, basic (in dollars per share)	$ (1.04)			$ (1.08)			$ (3.09)	$ (2.62)
Net loss per share, diluted (in dollars per share)	$ (1.04)			$ (1.08)			$ (3.09)	$ (2.62)