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Pension Plans - Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost (Detail)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan Weighted Average Assumptions Used In Calculating Net Periodic Benefit Cost [Abstract]      
Discount rate 4.25% 4.25% 4.00%
Rate of compensation increase 0.00% 0.00% 0.00%
Expected long-term return on plan assets 8.00% 8.00% 8.00%