Redeemable Convertible Preferred Stock and Common Stock - Preferred 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
Redeemable Convertible Preferred Stock and Common Stock
Preferred Stock Authorized	138,821,984			85,299,885
Preferred Stock Issued	138,821,984			85,299,885
Preferred stock outstanding	138,821,984	138,821,984	138,821,984	85,299,885	85,299,885	61,284,517	61,284,517	37,269,149
Carrying Value	$ 197,489	$ 197,489	$ 197,489	$ 81,658	$ 81,658	$ 56,794	$ 56,794	$ 31,816
Liquidation Preference	$ 204,627			$ 88,377
Common stock issuable upon conversion	19,185,183			11,788,435
Series Seed redeemable convertible preferred stock
Redeemable Convertible Preferred Stock and Common Stock
Preferred Stock Authorized	2,420,746			2,420,746
Preferred Stock Issued	2,420,746			2,420,746
Preferred stock outstanding	2,420,746			2,420,746
Carrying Value	$ 2,061			$ 2,061
Liquidation Preference	$ 2,100			$ 2,100
Common stock issuable upon conversion	334,547			334,547
Series A Redeemable Convertible Preferred Stock
Redeemable Convertible Preferred Stock and Common Stock
Preferred Stock Authorized	82,879,139			82,879,139
Preferred Stock Issued	82,879,139			82,879,139
Preferred stock outstanding	82,879,139			82,879,139
Carrying Value	$ 79,597			$ 79,597
Liquidation Preference	$ 86,277			$ 86,277
Common stock issuable upon conversion	11,453,888			11,453,888
Series B Redeemable Convertible Preferred Stock
Redeemable Convertible Preferred Stock and Common Stock
Preferred Stock Authorized	53,522,099
Preferred Stock Issued	53,522,099
Preferred stock outstanding	53,522,099
Carrying Value	$ 115,831
Liquidation Preference	$ 116,250
Common stock issuable upon conversion	7,396,748