Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity - Summary of Estimated Weighted-Average Assumptions (Detail)

v3.10.0.1
Stockholders' Equity - Summary of Estimated Weighted-Average Assumptions (Detail) - Employees - USD ($)
9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term (years) 4 years 7 months 6 days 4 years 6 months
Expected volatility 73.40% 69.10%
Risk-free interest rate 2.70% 1.80%
Expected dividend yield 0.00% 0.00%
Weighted-average estimated grant date fair value per share $ 22.86 $ 8.88
Options granted 2,633,950 1,155,900
Total estimated grant date fair value $ 60,212,000 $ 10,264,000