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Share-Based Compensation (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award      
Future awards shares under approved incentive compensation plans 784,254    
Share-based compensation maximum option term (in years) 10 years    
Contributions made by the company to 401(k) plan $ 1.7 $ 1.5 $ 1.3
Stock Option Awards      
Share-based Compensation Arrangement by Share-based Payment Award      
Unearned share-based compensation associated with awards $ 2.7    
Unrecognized compensation cost related to stock options expected to be recognized over a weighted-average period 5 years 1 month 6 days    
Restricted Stock Awards      
Share-based Compensation Arrangement by Share-based Payment Award      
Unearned share-based compensation associated with awards $ 19.5 $ 19.8  
Unrecognized compensation cost related to stock options expected to be recognized over a weighted-average period 2 years 8 months 12 days    
Restricted Share Units      
Share-based Compensation Arrangement by Share-based Payment Award      
Vesting period (in years) 3 years    
Phantom Stock Awards | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award      
Vesting period (in years) 5 years    
Phantom Stock Awards | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award      
Vesting period (in years) 7 years