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Stock-Based Incentive Plan - Aggregated Assumptions Used to Estimate Fair Value of Options Granted (Detail) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Share-based Payment Arrangement [Abstract]    
Expected option life in years - weighted average 6 years 7 months 6 days 6 years 10 months 24 days
Risk free interest rate - weighted average 2.80% 2.30%
Expected dividend yield - weighted average 2.81% 2.84%
Expected volatility - weighted average 27.15% 29.75%
Fair value of options $ 6.46 $ 6.72