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Stockholders Equity and Stock Options - Summary of Stock Option Activity (Detail) - USD ($)
$ / shares in Units, $ in Millions
9 Months Ended 12 Months Ended
Sep. 30, 2021
Dec. 31, 2020
Stockholders Equity Note [Abstract]    
Number of shares, Outstanding 2,008,902  
Number of shares, Granted 617,150  
Number of shares, Forfeited (80,090)  
Number of shares, Outstanding 2,545,962 2,008,902
Number of shares, Exercisable as of September 30, 2021 944,249  
Number of shares, Vested and expected to vest as of September 30, 2021 2,545,962  
Weighted average exercise price, balance $ 22.31  
Weighted average exercise price, Granted 15.62  
Weighted average exercise price, Forfeited 62.42  
Weighted average exercise price, balance 19.43 $ 22.31
Weighted average exercise price, Exercisable as of September 30, 2021 29.29  
Weighted average exercise price, Vested and expected to vest as of September 30, 2021 $ 19.43  
Weighted average remaining contractual term, outstanding 7 years 9 months 18 days 7 years 10 months 24 days
Weighted average remaining contractual term, Exercisable as of September 30, 2021 5 years 9 months 18 days  
Weighted average remaining contractual term, Vested and expected to vest as of September 30, 2021 7 years 9 months 18 days  
Aggregate intrinsic value, outstanding $ 0.4  
Aggregate intrinsic value, Vested and expected to vest as of September 30, 2021 $ 0.4