Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation - Summary of Fair Values of Stock Options Granted and Assumptions used in Black-Scholes Model (Detail)

v3.19.3
Stock-Based Compensation - Summary of Fair Values of Stock Options Granted and Assumptions used in Black-Scholes Model (Detail) - Stock Options [Member] - USD ($)
9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Estimated fair values of stock options granted $ 10,700 $ 9,570
Risk-free interest rate, minimum 1.90% 2.20%
Risk-free interest rate, maximum 2.50% 2.80%
Expected volatility, minimum 77.90% 40.90%
Expected volatility, maximum 78.90% 57.20%
Minimum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected term (in years) 6 years 9 months 18 days 5 years 7 months 6 days
Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected term (in years) 10 years 10 years