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Weighted-Average Assumptions Used for Stock Options Granted (Detail) - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term in years 4 years 3 months 4 years 3 months 4 years 3 months
Risk-free interest rate 1.25% 1.35% 0.82%
Expected volatility 20.96% 22.07% 24.56%
Expected dividend yield 2.29% 1.69% 2.20%
Grant date fair value $ 17.17 $ 15.75 $ 13.33