Net Loss per Share - Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2022	Sep. 30, 2021
Numerator:
Net loss	$ (64,919)	$ (66,632)	$ (67,993)	$ (77,975)	$ (75,970)	$ (72,593)	$ (199,544)	$ (226,538)
Denominator:
Weighted-average common shares outstanding	72,236,283			71,286,685			71,752,246	70,296,187
Less: weighted-average common shares subject to vesting				(1,176,547)				(1,305,897)
Weighted-average common shares used to compute basic net loss per share	72,236,283			70,110,138			71,752,246	68,990,290
Weighted-average common shares used to compute diluted net loss per share	72,236,283			70,110,138			71,752,246	68,990,290
Net loss per share: basic	$ (0.90)			$ (1.11)			$ (2.78)	$ (3.28)
Net loss per share: diluted	$ (0.90)			$ (1.11)			$ (2.78)	$ (3.28)