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Stock-Based Compensation - Additional Information (Detail)
$ / shares in Units, term in Millions, $ in Millions
12 Months Ended
Dec. 31, 2019
USD ($)
term
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2017
USD ($)
$ / shares
shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Incentive Plan, common stock available for issuance | shares 3,400,000    
Number of long term incentive plans | term 2    
Incentive Plan, options vesting period 3 years    
Unrecognized compensation cost, weighted-average recognition period 1 year 9 months 18 days    
Incentive Plan, options maturity period 10 years    
Incentive Plan, weighted-average grant date fair value of stock options granted | $ / shares $ 11.36 $ 14.14 $ 13.49
Unrecognized compensation cost related to unvested option $ 4.9    
Fair value of options vested 7.1 $ 6.7 $ 6.8
Intrinsic value of stock options exercised $ 26.0 8.7 70.6
Performance Condition Achievement      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Vested | shares (186,249)    
Restricted Stock Units      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Compensation costs classified as liability $ 1.4    
Incentive Plan, options vesting period 3 years    
Unrecognized pre-tax compensation cost $ 19.2    
Fair value of performance share awards vested $ 15.2 $ 22.2 $ 20.3
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 $ 7.0    
Unrecognized compensation cost, weighted-average recognition period 1 year 9 months 18 days    
Fair value of performance share awards vested $ 8.3    
Vested | shares (126,700)    
Director Awards      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Stock awards issued | shares 21,746 19,109 15,311
Common stock issued to outside directors | $ / shares $ 54.48 $ 54.93 $ 63.43