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Employee Benefit Plans (Pension Benefit Plan) - Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost (Detail)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Compensation And Retirement Disclosure [Abstract]      
Discount rates 1.90% 2.64% 2.20%
Rate of compensation increase 2.00% 2.00% 2.25%
Expected long-term rates of return 5.90% 5.40% 5.40%