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Share-Based Compensation - Other Information Pertaining to Term-Based Options (Detail) - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Term Based Stock Options [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 $ 21.15 $ 16.12 $ 7.80