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Redeemable convertible preferred stock (Details) - USD ($) $ / shares in Units, $ in Thousands |  |  | 1 Months Ended | 3 Months Ended | 9 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Jul. 14, 2021 | Jun. 25, 2021 | Mar. 31, 2021 | Apr. 30, 2020 | Mar. 31, 2021 | Jun. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020 | Jul. 19, 2021 | Dec. 31, 2020 | Mar. 31, 2020 | Feb. 29, 2020 | Dec. 31, 2019
Redeemable convertible preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |
Temporary equity share price (in dollars per share) |  |  |  |  |  |  | $ 0.01 |  | $ 0.01 | $ 0.01 |  |  |
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs |  |  |  |  |  |  | $ 79,743 | $ 49,935 |  |  |  |  |
Preferred stock, authorized (in shares) |  |  |  |  |  |  | 0 |  | 10,000,000 | 161,455,689 |  |  |
Peferred stock , par value (in shares) |  |  |  |  |  |  | $ 0.01 |  | $ 0.01 | $ 0.01 |  |  |
Preferred stock ,outstanding (in shares) |  |  | 155,521,633 |  | 155,521,633 | 133,021,640 | 0 | 133,021,640 |  | 133,021,640 | 78,757,540 |  | 78,757,540
Convertible Notes |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  |  |  |  |  |  |  |  |  | $ 7,100 |
Series C1 And C2 Redeemable Convertible Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |
Temporary equity share price (in dollars per share) |  |  |  | $ 1.15 |  |  |  |  |  |  |  |  |
Issuance costs |  |  |  | $ 600 |  |  |  |  |  |  |  |  |
Peferred stock , par value (in shares) |  |  |  | $ 1.15 |  |  |  |  |  |  |  |  |
Series C1 Redeemable Convertible Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |
Shares issued |  |  |  | 23,611,208 |  | 23,611,208 |  |  |  |  |  |  |
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs |  |  |  | $ 27,200 |  |  |  |  |  |  |  |  |
Preferred stock, authorized (in shares) |  |  |  |  |  |  |  |  |  | 57,372,796 |  |  |
Preferred stock ,outstanding (in shares) |  |  |  |  |  |  |  |  |  | 33,962,271 |  |  |
Series C1 Redeemable Convertible Preferred Stock | Convertible Notes |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |
Number of stock issued upon conversion of convertible preferred stock |  |  |  | 10,351,063 |  |  |  |  |  |  |  |  |
Long-term debt |  |  |  | $ 9,500 |  |  |  |  |  |  |  |  |
Series C2 Redeemable Convertible Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |
Shares issued |  |  |  | 20,301,829 |  | 20,301,829 |  |  |  |  |  |  |
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs |  |  |  | $ 23,300 |  |  |  |  |  |  |  |  |
Number of shares exchanged |  | 11,437,301 |  |  |  |  |  |  |  |  |  |  |
Preferred stock, authorized (in shares) |  |  |  |  |  |  |  |  |  | 20,301,829 |  |  |
Preferred stock ,outstanding (in shares) |  |  |  |  |  |  |  |  |  | 20,301,829 |  |  |
Series D1 and D2 Redeemable Convertible Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |
Temporary equity share price (in dollars per share) |  |  | $ 3.60 |  | $ 3.60 |  |  |  |  |  |  |  |
Issuance costs |  |  | $ 2,700 |  |  |  |  |  |  |  |  |  |
Peferred stock , par value (in shares) |  |  | $ 3.60 |  | $ 3.60 |  |  |  |  |  |  |  |
Series D1 Redeemable Convertible Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |
Shares issued |  |  | 22,086,725 |  | 22,086,725 |  |  |  |  |  |  |  |
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs |  |  | $ 79,500 |  |  |  |  |  |  |  |  |  |
Series D2 Redeemable Convertible Preferred Stock |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |
Shares issued |  |  | 413,268 |  | 413,268 |  |  |  |  |  |  |  |
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs |  |  | $ 1,500 |  |  |  |  |  |  |  |  |  |
Number of shares exchanged |  | 2,364,509 |  |  |  |  |  |  |  |  |  |  |
Common Class A |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion of Stock, Shares Issued | 24,200,920 |  |  |  |  |  |  |  |  |  |  |  |
Common Class B |  |  |  |  |  |  |  |  |  |  |  |  |
Redeemable convertible preferred stock |  |  |  |  |  |  |  |  |  |  |  |  |
Conversion of Stock, Shares Issued | 6,903,379 |  |  |  |  |  |  |  |  |  |  |  |

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