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Stock Incentive Plans and Stock Purchase Plan - Schedule of Activity and Certain Other Information Related to Stock Option Awards (Detail) - USD ($)
$ / shares in Units, $ in Millions
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Number of Shares, Outstanding at January 1, 2015 814,094    
Number of Shares, Exercised (228,707)    
Number of Shares, Outstanding at December 31, 2015 585,387 814,094  
Number of Shares, Exercisable at December 31, 2015 585,387    
Weighted Average Exercise Price, Outstanding at January 1, 2015 $ 27.57    
Weighted Average Exercise Price, Exercised 26.58    
Weighted Average Exercise Price, Outstanding at December 31, 2015 27.96 $ 27.57  
Weighted Average Exercise Price, Exercisable at December 31, 2015 $ 27.96    
Weighted Average Remaining Contractual Term (in years), Outstanding at December 31, 2015 2 years 8 months 12 days    
Weighted Average Remaining Contractual Term (in years), Exercisable at December 31, 2015 2 years 8 months 12 days    
Aggregate Intrinsic Value, Exercised $ 11.3 $ 38.8 $ 35.4
Aggregate Intrinsic Value, Outstanding at December 31, 2015 25.6    
Aggregate Intrinsic Value, Exercisable at December 31, 2015 $ 25.6