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) - Employees - USD ($)
6 Months Ended
Jun. 30, 2018
Jun. 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 73.50% 66.00%
Risk-free interest rate 2.60% 1.80%
Expected dividend yield 0.00% 0.00%
Weighted-average estimated grant date fair value per share $ 22.79 $ 8.89
Options granted 1,578,750 770,900
Total estimated grant date fair value $ 35,980,000 $ 6,853,000