Quarterly report pursuant to Section 13 or 15(d)

Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail)

v3.19.3
Stock Based Compensation - Weighted-Average Fair Value Valuation Assumptions (Detail) - Employee Stock Options - $ / shares
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Risk-free interest rate 1.87% 3.01% 2.47% 2.79%
Expected term (in years) 6 years 29 days 6 years 25 days 6 years 29 days 6 years 10 days
Dividend yield 0.00% 0.00% 0.00% 0.00%
Volatility 107.21% 109.00% 108.67% 107.00%
Weighted-average fair value of stock options granted $ 4.96 $ 4.50 $ 4.36 $ 5.82