Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity (Deficit) - Schedule of Stock Option Activity (Detail)

v3.8.0.1
Stockholders' Equity (Deficit) - Schedule of Stock Option Activity (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 9 Months Ended 12 Months Ended
Sep. 30, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Options Exercised (3,281)  
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 4,000,508  
Options Exercised (3,281)  
Options Forfeited / Cancelled (115,719)  
Options, Outstanding, Ending Balance 4,561,942 680,434
Options, Exercisable at September 30, 2017 1,661,125  
Weighted-Average Exercise Price, Outstanding, Beginning Balance $ 2.27  
Weighted-Average Exercise Price, Options Granted 14.66  
Weighted-Average Exercise Price, Options Exercised 1.70  
Weighted-Average Exercise Price, Options Forfeited / Cancelled 8.56  
Weighted-Average Exercise Price, Outstanding, Ending Balance $ 12.99 $ 2.27
Weighted-Average Remaining Contractual Term, Outstanding 8 years 11 months 23 days 8 years 5 months 27 days
Weighted-Average Aggregate Intrinsic Value $ 155,197 $ 3,031