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Employee Benefit Plans - Summary of Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost (Detail)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Pension Plan [Member]    
Weighted-average assumptions used to determine Net Periodic Benefit Cost    
Discount rate 1.80% 3.59%
Expected return on plan assets 0.00% 7.00%
Corridor 10.00% 10.00%
Supplemental Employee Retirement Plan [Member]    
Weighted-average assumptions used to determine Net Periodic Benefit Cost    
Discount rate 3.35% 3.80%
Corridor 10.00% 10.00%
Postretirement Benefits [Member]    
Weighted-average assumptions used to determine Net Periodic Benefit Cost    
Discount rate   4.00%
Corridor   10.00%