Annual report pursuant to Section 13 and 15(d)

Stock Plans - Schedule of Stock Option Activity (Detail)

v3.8.0.1
Stock Plans - Schedule of Stock Option Activity (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Weighted-Average Aggregate Intrinsic Value $ 44,712 $ 3,031
Weighted-Average Aggregate Intrinsic Value, Exercisable 19,433  
Weighted-Average Aggregate Intrinsic Value, Vested and expected to vest $ 43,994  
2014 Plan Stock Options/Stock Issuance Plan and 2017 Stock Incentive Plan [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Options, Outstanding, Beginning Balance 680,434  
Options Granted 4,383,208  
Options Exercised (80,829)  
Options Forfeited (161,346)  
Options Expired (18,873)  
Options, Outstanding, Ending Balance 4,802,594 680,434
Options,Exercisable at December 31, 2017 1,805,482  
Vested and expected to vest at December 31, 2017 4,715,202  
Weighted-Average Exercise Price, Outstanding, Beginning Balance $ 2.27  
Weighted-Average Exercise Price, Options Granted 15.27  
Weighted-Average Exercise Price, Options Exercised 1.62  
Weighted-Average Exercise Price, Options Forfeited 9.90  
Weighted-Average Exercise Price, Options Expired 1.50  
Weighted-Average Exercise Price, Outstanding, Ending Balance 13.89 $ 2.27
Weighted-Average Exercise Price, Exercisable 12.44  
Weighted-Average Exercise Price, Vested and expected to vest $ 13.87  
Weighted-Average Remaining Contractual Term, Outstanding 9 years 2 months 1 day 8 years 5 months 27 days
Weighted-Average Remaining Exercisable 8 years 10 months 6 days  
Weighted-Average Remaining Contractual Term, Vested and expected to vest 9 years 2 months 1 day