Quarterly report pursuant to Section 13 or 15(d)

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

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Stockholders' Equity - Summary of Estimated Weighted-Average Assumptions (Detail) - USD ($)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Options granted 719,950  
Employees    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Expected term (years) 4 years 6 months 4 years 4 months 24 days
Expected volatility 74.00% 69.20%
Risk-free interest rate 2.50% 1.90%
Expected dividend yield 0.00% 0.00%
Weighted-average estimated grant date fair value per share $ 20.39 $ 8.21
Options granted 719,950 155,100
Total estimated grant date fair value $ 14,680,000 $ 1,273,000