Redeemable Convertible Preferred Stock - Schedule of Temporary Equity by Stock (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Temporary Equity [Line Items]
Shares Authorized (in shares)	0			26,983,984
Shares Issued and Outstanding (in shares)	0	29,850,000	25,402,000	25,402,402	25,402,000	21,118,000	21,073,000	20,998,000
Carrying Value	$ 0	$ 328,564	$ 243,854	$ 243,854	$ 243,852	$ 173,677	$ 173,447	$ 173,068
Series A
Temporary Equity [Line Items]
Shares Authorized (in shares)				1,243,223
Shares Issued and Outstanding (in shares)				1,104,728
Carrying Value				$ 2,781
Series B
Temporary Equity [Line Items]
Shares Authorized (in shares)				1,841,805
Shares Issued and Outstanding (in shares)				1,543,804
Carrying Value				$ 5,404
Series C
Temporary Equity [Line Items]
Shares Authorized (in shares)				1,564,851
Shares Issued and Outstanding (in shares)				1,564,851
Carrying Value				$ 7,073
Series D
Temporary Equity [Line Items]
Shares Authorized (in shares)				8,245,295
Shares Issued and Outstanding (in shares)				7,547,542
Carrying Value				$ 36,879
Series E
Temporary Equity [Line Items]
Shares Authorized (in shares)				8,825,653
Shares Issued and Outstanding (in shares)				8,414,496
Carrying Value				$ 115,229
Series F
Temporary Equity [Line Items]
Shares Authorized (in shares)				5,263,157
Shares Issued and Outstanding (in shares)				5,226,981
Carrying Value				$ 76,488