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Weighted-Average Assumptions Used to Estimate Grant Date Fair Values for Stock Options Granted (Detail) - Employee Stock Option
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Volatility 35.11% 37.95%
Expected term (in years) 5 years 5 years
Dividend yield 2.05% 2.00%
Risk-free interest rate 1.40% 1.37%