Net Loss Per Share Attributable to Common Stockholders - Loss per Share (Details) - USD ($) $ / shares in Units, $ 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	$ (91,073)	$ (10,305)	$ 3,010	$ (41,612)	$ (12,786)	$ 2,778	$ (98,368)	$ (51,619)
Less: deemed dividend upon redemption of redeemable convertible preferred stock	0			0			(13,137)	0
Net loss attributable to common stockholders, basic	(91,073)			(41,612)			(111,505)	(51,619)
Net loss attributable to common stockholders, diluted	$ (91,073)			$ (41,612)			$ (111,505)	$ (51,619)
Denominator
Weighted average shares, basic (in shares)	62,887,161			53,179,523			56,985,960	52,818,555
Weighted average shares, diluted (in shares)	62,887,161			53,179,523			56,985,960	52,818,555
Earnings Per Share
Net loss per share attributable to common stockholders, basic (in dollars per share)	$ (1.45)			$ (0.78)			$ (1.96)	$ (0.98)
Net loss per share attributable to common stockholders, diluted (in dollars per share)	$ (1.45)			$ (0.78)			$ (1.96)	$ (0.98)