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Accounting for Stock Based Compensation - Summarizes Stock Appreciation Rights (SARs) Activity (Detail) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock Options Outstanding, beginning balance, Shares 869,000 1,653,000 2,652,142  
Granted, Shares 0 0 0  
Exercised, Shares (434,250) (428,250) (615,358)  
Forfeited, Shares (6,750) (355,750) (383,784)  
Stock Options Outstanding, ending balance, Shares 428,000 869,000 1,653,000 2,652,142
Exercisable, Ending Balance     338,625  
Stock Options Outstanding, beginning balance, Weighted-Average Exercise Price $ 37.87 $ 38.53 $ 35.34  
Exercised, Weighted-Average Exercise Price 38.12 38.66 24.01  
Forfeited, Weighted-Average Exercise Price 38.05 39.99 39.59  
Stock Options Outstanding, ending balance, Weighted-Average Exercise Price $ 37.61 $ 37.87 38.53 $ 35.34
Exercisable, Weighted Average Exercise Price     $ 37.87  
Stock Options Outstanding, Weighted-Average Remaining Contractual Term 3 years 2 months 12 days 3 years 6 months 3 days 4 years 3 months 10 days 4 years 9 months 3 days
Exercisable, Weighted-Average Remaining Contractual Term     3 years 1 month 9 days  
Outstanding, Aggregate Intrinsic Value $ 11,815 $ 5,172 $ 3,610 $ 6,964
Exercisable, Aggregate Intrinsic Value     $ 9,261  
Stock Appreciation Rights (SARs)        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Stock Options Outstanding, beginning balance, Shares 554,250 988,100 1,192,350  
Exercised, Shares (342,150) (179,500) (204,250)  
Forfeited, Shares (40,500) (254,350)    
Stock Options Outstanding, ending balance, Shares 171,600 554,250 988,100 1,192,350
Exercisable, Ending Balance     131,350  
Stock Options Outstanding, beginning balance, Weighted-Average Exercise Price $ 39.41 $ 40.61 $ 38.17  
Exercised, Weighted-Average Exercise Price 38.22 32.84 26.35  
Forfeited, Weighted-Average Exercise Price 44.39 42.63    
Stock Options Outstanding, ending balance, Weighted-Average Exercise Price $ 40.60 $ 39.41 40.61 $ 38.17
Exercisable, Weighted Average Exercise Price     $ 41.39  
Stock Options Outstanding, Weighted-Average Remaining Contractual Term 2 years 5 months 8 days 2 years 10 months 2 days 3 years 6 months 25 days 4 years 4 months 9 days
Exercisable, Weighted-Average Remaining Contractual Term     3 years 1 month 2 days  
Outstanding, Aggregate Intrinsic Value $ 4,224 $ 2,981 $ 2,064 $ 2,278
Exercisable, Aggregate Intrinsic Value     $ 3,131