Annual report pursuant to Section 13 and 15(d)

Stock Plan and Stock-Based Compensation - Estimated Weighted-Average Grant Date Fair Value (Detail)

v3.10.0.1
Stock Plan and Stock-Based Compensation - Estimated Weighted-Average Grant Date Fair Value (Detail) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term 6 years 2 months 12 days 6 years 6 years 1 month 6 days
Expected volatility 77.00% 84.00% 80.00%
Risk-free interest rate 2.62% 2.15% 1.57%
Expected dividend yield     0.00%
Weighted-average grant date fair value per share $ 8.14 $ 3.36 $ 0.89
Performance Option [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term     5 years 1 month 6 days
Expected volatility     85.00%
Risk-free interest rate     1.56%
Expected dividend yield     0.00%
Weighted-average grant date fair value per share     $ 1.20