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Stock-based Compensation Plans - Summary of SARs Outstanding and Exercisable (Detail) - Stock Appreciation Rights (SARs) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]        
Number of outstanding Number of exercisable, Shares 382,779      
Weighted Average Remaining Contractual Life (in years) 4 months 9 days      
Weighted Average Exercise Price, Outstanding $ 76.54 $ 69.08 $ 63.73 $ 59.80
Number of exercisable, Shares 382,779      
Weighted Average Exercise Price, Exercisable $ 76.54      
Range of Exercise Prices One        
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]        
Exercise Price, Minimum 70.00      
Exercise Price, Maximum $ 79.99      
Number of outstanding Number of exercisable, Shares 380,879      
Weighted Average Remaining Contractual Life (in years) 4 months 9 days      
Weighted Average Exercise Price, Outstanding $ 76.51      
Number of exercisable, Shares 380,879      
Weighted Average Exercise Price, Exercisable $ 76.51      
Range of Exercise Prices Two        
Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range [Line Items]        
Exercise Price, Minimum 80.00      
Exercise Price, Maximum $ 81.15      
Number of outstanding Number of exercisable, Shares 1,900      
Weighted Average Remaining Contractual Life (in years) 8 months 8 days      
Weighted Average Exercise Price, Outstanding $ 81.15      
Number of exercisable, Shares 1,900      
Weighted Average Exercise Price, Exercisable $ 81.15