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Stock-Based Compensation - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Incentive Plan, common stock available for issuance 7,000,000    
Incentive Plan, options vesting period 3 years    
Incentive Plan, options maturity period 10 years    
Incentive Plan, weighted-average grant date fair value of stock options granted $ 11.58 $ 12.72 $ 9.02
Unrecognized compensation cost related to unvested option $ 6.4    
Fair value of options vested 7.8 $ 9.8 $ 12.4
Intrinsic value of stock options exercised 78.0 63.4 97.1
Restricted Stock Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unrecognized pre-tax compensation cost $ 17.8    
Unrecognized compensation cost, weighted-average recognition period 1 year 10 months 24 days    
Fair value of performance share awards vested $ 24.9 $ 31.1 $ 26.9
Stock Option Awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unrecognized compensation cost, weighted-average recognition period 1 year 7 months 6 days    
Performance Awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unrecognized pre-tax compensation cost $ 6.4    
Unrecognized compensation cost, weighted-average recognition period 1 year 7 months 6 days    
Fair value of performance share awards vested $ 11.8    
Director Awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock awards issued 19,695 22,654 24,672
Common stock issued to outside directors $ 46.21 $ 40.01 $ 36.47