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Employee Benefit Plans - Summary of Weighted-Average Assumptions for Disclosure (Detail)
Dec. 31, 2017
Dec. 31, 2016
Pension Plan [Member]    
Weighted-average assumptions for Disclosure    
Discount rate 1.80% 3.62%
Rate of compensation increase 0.00% 0.00%
Supplemental Employee Retirement Plan [Member]    
Weighted-average assumptions for Disclosure    
Discount rate 3.35% 3.80%
Rate of compensation increase 0.00% 0.00%
Postretirement Benefits [Member]    
Weighted-average assumptions for Disclosure    
Discount rate 3.75% 4.00%
Rate of compensation increase 0.00% 0.00%