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Assumptions Used in Black-Scholes Model to Determine Fair Value for Stock Option Awards Granted (Detail)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Volatility 28.00% 31.00% 33.00%
Interest rate 1.00% 1.00% 1.00%
Expected life (years) 3 years 4 months 24 days 3 years 4 months 24 days 3 years 4 months 24 days
Forfeiture rate 10.00% 10.00% 10.00%
Dividend yield 0.40% 0.40% 0.40%