Quarterly report pursuant to Section 13 or 15(d)

Stock Plans - Schedule of Stock Option Activity (Detail)

v3.10.0.1
Stock Plans - Schedule of Stock Option Activity (Detail) - USD ($)
 6 Months Ended 12 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Weighted-Average Aggregate Intrinsic Value $ 14,237 $ 44,974
Weighted-Average Aggregate Intrinsic Value, Exercisable $ 8,364  
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 4,802,594  
Options Granted 3,772,666  
Options Exercised (121,158)  
Options Forfeited (361,072)  
Options Expired (1,425)  
Options, Outstanding, Ending Balance 8,091,605 4,802,594
Options, Exercisable at June 30, 2018 2,266,950  
Weighted-Average Exercise Price, Outstanding, Beginning Balance $ 13.89  
Weighted-Average Exercise Price, Options Granted 20.39  
Weighted-Average Exercise Price, Options Exercised 3.83  
Weighted-Average Exercise Price, Options Forfeited 17.03  
Weighted-Average Exercise Price, Options Expired 12.24  
Weighted-Average Exercise Price, Outstanding, Ending Balance 16.93 $ 13.89
Weighted-Average Exercise Price, Exercisable $ 13.13  
Weighted-Average Remaining Contractual Term, Outstanding 9 years 2 months 23 days 9 years 2 months 1 day
Weighted-Average Remaining Exercisable 8 years 6 months 10 days