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Assumptions to Estimate Fair Value for Stock Options at Grant Date (Detail) - Time Vested Stock Options
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate, minimum 0.17% 1.57%
Risk-free interest rate, maximum 1.22% 2.22%
Expected volatility, minimum 46.00% 39.00%
Expected volatility, maximum 54.00% 50.00%
Weighted average expected volatility 52.00% 38.00%
Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life (in years) 4 years 4 years
Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life (in years) 6 years 3 months 6 years 3 months