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Share-Based Payments - Weighted Average Assumptions Used to Determine Fair Value of Options Granted (Detail)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Expected life (in years) 4 years 10 months 24 days 4 years 10 months 24 days 4 years 10 months 24 days
Risk-free interest rate 1.50% 1.60% 1.50%
Volatility factor 23.10% 23.70% 31.80%
Dividend yield 6.50% 4.30% 3.40%