Quarterly report pursuant to Section 13 or 15(d)

Equity Instruments - Conversion of Redeemable Convertible Preferred Stock into Common Stock at a conversion ratio of 3:1 and Issuance of Series??D Redeemable Convertible Preferred Stock (Details)

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Equity Instruments - Conversion of Redeemable Convertible Preferred Stock into Common Stock at a conversion ratio of 3:1 and Issuance of Series D Redeemable Convertible Preferred Stock (Details)
$ / shares in Units, $ in Thousands
 9 Months Ended
Apr. 13, 2020
USD ($)
$ / shares
shares
Sep. 30, 2021
USD ($)
$ / shares
Sep. 30, 2020
USD ($)
shares
Jun. 30, 2021
USD ($)
Dec. 31, 2020
USD ($)
$ / shares
Jun. 30, 2020
USD ($)
Dec. 31, 2019
USD ($)
Temporary Equity [Line Items]              
Conversion ratio 3            
Number of shares converted | shares     4,456,248        
Carrying value   $ 0 $ 118,374 $ 123,704 $ 123,704 $ 118,374 $ 101,858
Common stock, fair value $ 200            
Extinguishment of redeemable convertible preferred stock $ 13,100   13,274        
Decrease in redeemable convertible preferred stock resulting from the conversion     $ (13,274)        
Number of shares issued | shares     75,660,962        
Original issue price per share (in usd per share) | $ / shares $ 0.37534 $ 0          
Proceeds from issuance of redeemable convertible preferred stock   $ 0 $ 28,278        
Additional Paid-In Capital              
Temporary Equity [Line Items]              
Extinguishment of redeemable convertible preferred stock $ 200   223        
Accumulated Deficit              
Temporary Equity [Line Items]              
Extinguishment of redeemable convertible preferred stock $ 13,100   $ 13,051        
Series A Redeemable Convertible Preferred Stock              
Temporary Equity [Line Items]              
Number of shares converted | shares 2,167,198            
Carrying value         $ 17,030    
Original issue price per share (in usd per share) | $ / shares         $ 2.928    
Series B Redeemable Convertible Preferred Stock              
Temporary Equity [Line Items]              
Number of shares converted | shares 1,999,348            
Carrying value         $ 32,176    
Original issue price per share (in usd per share) | $ / shares         $ 3.851    
Series C Redeemable Convertible Preferred Stock              
Temporary Equity [Line Items]              
Number of shares converted | shares 289,702            
Carrying value         $ 39,378    
Original issue price per share (in usd per share) | $ / shares         $ 5.524    
Common Stock              
Temporary Equity [Line Items]              
Number of shares to be converted into | shares 1,210,513            
Redeemable Convertible Preferred Stock              
Temporary Equity [Line Items]              
Carrying value $ 13,300            
Decrease in redeemable convertible preferred stock resulting from the conversion $ 13,300            
Series D Redeemable Convertible Preferred Stock              
Temporary Equity [Line Items]              
Carrying value         $ 35,120    
Number of shares issued | shares 44,794,885            
Original issue price per share (in usd per share) | $ / shares         $ 0.375    
Proceeds from issuance of redeemable convertible preferred stock $ 16,800