Net Loss Per Share Attributable to Common Stockholders - Reconciliation of Numerator and Denominator Used in Calculation 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	$ (16,534)	$ (17,001)	$ 11,029	$ (13,255)	$ (15,522)	$ (14,023)	$ (22,506)	$ (42,800)
Add: accretion to redemption value and cumulative dividends on redeemable convertible preferred shares				(1,375)				(4,078)
Net loss attributable to common stockholders	$ (16,534)			$ (14,630)			$ (22,506)	$ (46,878)
Weighted-average common shares outstanding used to calculate net loss per share attributable to common stockholders:
Basic	35,445,504			1,714,285			16,592,746	1,561,242
Diluted	35,445,504			1,714,285			16,592,746	1,561,242
Net loss per share, attributable to common stockholders:
Basic	$ (0.47)			$ (8.53)			$ (1.36)	$ (30.03)
Diluted	$ (0.47)			$ (8.53)			$ (1.36)	$ (30.03)