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, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net loss	$ (13,693)	$ (51,065)	$ (8,706)	$ (2,668)	$ (4,838)	$ (3,083)	$ (73,464)	$ (10,589)
Denominator:
Weighted average common shares outstanding	31,095,610			1,718,510			11,620,515	1,706,784
Less: weighted average unvested common stock issued upon early exercise of common stock options	(114,169)			(160,618)			(121,188)	(171,873)
Less: weighted average unvested founder shares of common stock				(29,382)				(113,029)
Weighted average shares used to compute net loss per share, basic and diluted	30,981,441			1,528,510			11,499,327	1,421,882
Net loss per share, basic and diluted	$ (0.44)			$ (1.75)			$ (6.39)	$ (7.45)