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Schedule of Estimated Fair Value of Stock Options Grant Using Black Scholes Option Pricing Model (Detail) - Stock Options
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award      
Expected life (years) 5 years 4 years 4 years
Risk-free interest rate 1.40% 1.10% 1.20%
Volatility-historical 32.90% 33.40% 38.80%
Dividend yield 1.24% 1.33% 1.25%