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Stockholders’ (Deficit) Equity and Stock-Based Compensation - Stock option activity, narrative (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Employees    
Class of Stock [Line Items]    
Weighted-average grant-date fair value of options granted (in dollars per share) $ 3.56 $ 0.45
Weighted-average grant-date fair value of options forfeited (in dollars per share) 2.20 0.38
Weighted-average grant-date fair value of options vested (in dollars per share) $ 1.20 $ 0.30
Total fair value of options vested $ 7.1 $ 0.9
Aggregate intrinsic value of options exercised $ 103.4 $ 0.5
Common Stock | 2021 Equity Incentive Plan    
Class of Stock [Line Items]    
Percent of possible increase in shares available for issuance 5.00%  
Preferred Stock | Volta Charter    
Class of Stock [Line Items]    
Number of shares authorized (in shares) 10,000,000