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Stock Incentive Plans and Stock Purchase Plans - Schedule of Activity and Certain Other Information Related to Stock Option Awards (Detail) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Number of Shares, Outstanding at January 1, 2018 246,342    
Number of Shares, Exercised (133,366)    
Number of Shares, Outstanding at December 31, 2018 112,976 246,342  
Number of Shares, Exercisable at December 31, 2017 112,976    
Weighted Average Exercise Price, Outstanding at January 1, 2018 $ 27.51    
Weighted Average Exercise Price, Exercised 27.38    
Weighted Average Exercise Price, Outstanding at December 31, 2018 27.65 $ 27.51  
Weighted Average Exercise Price, Exercisable at December 31, 2018 $ 27.65    
Weighted Average Remaining Contractual Term (in years), Outstanding at December 31, 2018 1 year 3 months 18 days    
Weighted Average Remaining Contractual Term (in years), Exercisable at December 31, 2018 1 year 3 months 18 days    
Aggregate Intrinsic Value, Exercised $ 2.8 $ 5.5 $ 6.8
Aggregate Intrinsic Value, Outstanding at December 31, 2018 0.7    
Aggregate Intrinsic Value, Exercisable at December 31, 2018 $ 0.7