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Share-Based Compensation - Weighted-Average Assumptions Used for Grants of Stock Options and SARs (Detail) - SARs - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected dividend yield 0.00% 0.00% 0.00%
Forfeiture rate 8.00% 8.20% 8.40%
Volatility 42.51% 36.79% 35.93%
Risk free interest rate 0.24% 2.28% 2.96%
Expected weighted-average life 4 years 4 years 7 days 4 years 1 month 9 days
Weighted-average grant date fair value of SARs granted (per underlying share) (in USD per share) $ 79.47 $ 64.17 $ 47.63