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Benefit Plans - Schedule of Weighted-Average Assumptions Used to Determine Fair Value of Option Granted (Detail)
12 Months Ended
Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]  
Expected term (in years) 5 years
Expected volatility 26.10%
Expected dividend yields 3.00%
Risk-free interest rates 2.00%