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Share-Based Compensation - Fair Value of Options Granted (Detail)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]      
Dividend yields 2.34% 2.35% 2.01%
Volatility factors of expected market price of common stock 28.60% 28.97% 29.54%
Risk-free interest rates 1.83% 2.10% 2.66%
Expected life of options 8 years 8 years 8 years