Annual report pursuant to Section 13 and 15(d)

Stock Plans - Schedule of Fair Value Assumptions (Detail)

v3.19.1
Stock Plans - Schedule of Fair Value Assumptions (Detail) - 2014 Plan Stock Options/Stock Issuance Plan and 2017 Stock Incentive Plan [Member]
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Minimum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected term (in years) 6 years 3 days 5 years 9 months 29 days
Expected volatility 53.00% 52.00%
Risk-free interest rate 2.63% 1.79%
Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected term (in years) 6 years 25 days 6 years 3 months 21 days
Expected volatility 69.00% 65.00%
Risk-free interest rate 3.80% 2.20%