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Share-Based Compensation - Other Information Pertaining to RSUs (Detail) - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Restricted Stock Units (RSUs) [Member] | Share Based Compensation Plans [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average grant date fair value per share $ 69.57 $ 50.00 $ 35.55