Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation - Summary of Stock Option Activity (Detail)

v3.8.0.1
Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]    
Number of shares, Outstanding, Beginning Balance 1,930,600  
Number of shares, Granted 2,120,347  
Number of shares, Exercised (68,780)  
Number of shares, Canceled (98,735)  
Number of shares, Outstanding, Ending Balance 3,883,432 1,930,600
Number of shares, Exercisable at September 30, 2017 1,244,968  
Weighted average exercise price per share, Granted $ 13.29  
Weighted average exercise price per share, Exercised 3.95  
Weighted average exercise price per share, Canceled 1.23  
Weighted average exercise price per share outstanding 9.16 $ 4.45
Weighted average exercise price per share Exercisable $ 5.20  
Aggregate intrinsic value, Outstanding $ 49,965  
Aggregate intrinsic value, Exercisable $ 20,949  
Weighted average remaining contractual life, Outstanding 8 years 9 months 18 days 9 years 1 month 6 days
Weighted average remaining contractual life, Exercisable 8 years 1 month 6 days