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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, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award      
Expected life (years) 5 years 5 years 5 years
Risk-free interest rate 2.40% 2.00% 1.40%
Volatility-historical 26.40% 27.80% 32.90%
Dividend yield 0.80% 1.00% 1.20%