Annual report pursuant to Section 13 and 15(d)

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

v3.19.1
Stock-Based Compensation - Summary of Fair Values of Stock Options Granted and Assumptions used in Black-Scholes Model (Detail) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Estimated fair values of stock options granted $ 9,090 $ 2,420 $ 5,030
Risk-free interest rate, minimum 2.20% 1.30% 0.60%
Risk-free interest rate, maximum 3.00% 2.40%  
Expected volatility, minimum 40.90% 27.40% 30.00%
Expected volatility, maximum 57.20% 45.10%  
Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term (in years) 5 years 7 months 6 days 1 year 2 months 12 days 5 years 9 months 18 days
Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term (in years) 10 years 10 years 6 years 2 months 12 days