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Stock-based Compensation - Summary of Restricted Stock Unit Activity (Detail) - Restricted stock units
9 Months Ended
Sep. 30, 2021
$ / shares
shares
Number of Shares  
Unvested at beginning of period (in shares) | shares 2,499,000
Granted (in shares) | shares 1,978,000
Cancelled/forfeited (in shares) | shares (201,000)
Vested (in shares) | shares (662,000)
Unvested at ending of period (in shares) | shares 3,614,000
Weighted- Average Grant- Date Fair Value  
Unvested at beginning of period (in dollars per share) | $ / shares $ 9.53
Granted (in dollars per share) | $ / shares 18.87
Cancelled/forfeited (in dollars per share) | $ / shares 11.29
Vested (in dollars per share) | $ / shares 19.34
Unvested at ending of period (in dollars per share) | $ / shares $ 20.60