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Stock-Based Compensation - Performance Stock Units Unvested Roll Forward (Detail) - Performance Stock Unit Plan [Member] - $ / shares
shares in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unvested Beginning balance, Shares 105    
Shares granted 58 13 40
Shares Vested (36)    
Shares Forfeited (32)    
Unvested Ending balance, Shares 95 105  
Weighted-average grant date fair value per share of shares unvested at beginning of period $ 233.11    
Weighted-average grant date fair value per share of shares granted 190.45    
Weighted-average grant date fair value per share of shares vested 184.51    
Weighted-average grant date fair value per share of shares forfeited 218.63    
Weighted-average grant date fair value per share of shares unvested at end of period $ 230.36 $ 233.11