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Stock-Based Compensation Plans - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 12 Months Ended
Jan. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of stock options granted since 2003   0    
Stock options outstanding   0    
Compensation expense related to share-based compensation plans   $ 9,873 $ 8,479 $ 7,833
Compensation expense related to share-based compensation plans, net of tax   $ 6,500 5,200 5,000
Unrecognized compensation cost weighted average period recognized (years)   2 years 11 months 26 days    
Restricted Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Total fair value of restricted shares vested   $ 10,400 $ 7,500 $ 8,700
Unrecognized compensation cost related to non-vested share-based compensation   $ 25,500    
Restricted stock grants   428,333 420,368 338,531
Restricted stock grants, Weighted average grant date fair value   $ 43.31 $ 33.46 $ 37.60
Restricted Stock [Member] | Subsequent Event        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock grants, Weighted average grant date fair value $ 49.20      
Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock vesting period   3 years    
Minimum [Member] | Restricted Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock vesting period   3 years 3 years 3 years
Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock vesting period   5 years    
Maximum [Member] | Restricted Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock vesting period   5 years 5 years 5 years
Two Thousand Two Stock Incentive Plan [Member] | Class A Common Stock [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares authorized and available under long-term incentive plan   707,273    
Non-employee Directors [Member] | Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock vesting period   1 year    
Non-employee Directors [Member] | Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock vesting period   3 years    
Two Thousand Seventeen Stock Incentive Plan [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares available for future grant   1,948,363    
Employees [Member] | Restricted Stock [Member] | Subsequent Event        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock grants 323,347      
Employees [Member] | Performance Shares | Subsequent Event        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock grants 89,143      
Employees [Member] | Time Based Shares | Subsequent Event        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock grants 234,204      
Employees [Member] | Minimum [Member] | Restricted Stock [Member] | Subsequent Event        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock vesting period 3 years      
Employees [Member] | Maximum [Member] | Restricted Stock [Member] | Subsequent Event        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock vesting period 5 years      
Outside Directors [Member] | Restricted Stock [Member] | Subsequent Event        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Restricted stock vesting period 1 year      
Restricted stock grants 33,000