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Stock-Based Compensation - Schedule of Stock Option Activity (Detail) - 2013 and 2018 Equity Incentive Plan [Member] - USD ($)
9 Months Ended
Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Number of shares, Outstanding Beginning Balance 1,529,883
Number of shares, Granted 647,575
Number of shares, Exercised (40,041)
Number of shares, Forfeitures (151,216)
Number of shares, Outstanding Ending Balance 1,986,201
Number of shares, Options vested and exercisable Ending Balance 584,780
Weighted average exercise price, Outstanding Beginning Balance $ 8.03
Weighted average exercise price, Granted 10.74
Weighted average exercise price, Exercised 5.49
Weighted average exercise price, Forfeitures 8.87
Weighted average exercise price, Outstanding Ending Balance 8.90
Weighted average exercise price, Options vested and exercisable Ending Balance $ 7.29
Weighted average remaining contractual life (in years), Outstanding 8 years 8 months 12 days
Weighted average remaining contractual life (in years), Options vested and exercisable 8 years 3 months 18 days
Aggregate intrinsic value, Outstanding Ending Balance $ 11,771,966
Aggregate intrinsic value, Options vested and exercisable Ending Balance $ 4,403,891