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Pensions and Other Post-retirement Benefits - Additional Information (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]      
Estimated contributions by employer to pension plans $ 7,100    
Percentage increase in health care benefit cost   6.50%  
Percentage decrease in health care benefits for successive year 0.50% 0.50%  
Estimated future percentage of health care benefits 4.50% 4.50%  
Increase in costs of covered health care benefits 6.50%    
Percentage of change in assumed health care cost trend rate 1.00%    
Increase or decrease in other postretirement obligations $ 1,000    
Increase or decrease in current year plan expense 130    
Defined contribution pension plan expense $ 9,000 $ 8,100 $ 5,100
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss), Immediate Recognition Percent Greater Than Actuarial Losses 10.00%    
Pension Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) $ 5,901 18,526 6,332
Service cost 11,125 11,023 10,417
Estimated benefit payments, year one 29,800    
Estimated benefit payments, year two 24,800    
Estimated benefit payments, year three 25,700    
Estimated benefit payments, year four 26,400    
Estimated benefit payments, year five 27,300    
Estimated benefit payments, five years thereafter 145,100    
Other Benefits      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) 1,509 516 1,021
Service cost 369 $ 403 $ 426
Estimated benefit payments, year one 2,800    
Estimated benefit payments, year two 2,700    
Estimated benefit payments, year three 2,800    
Estimated benefit payments, year four 2,600    
Estimated benefit payments, year five 2,300    
Estimated benefit payments, five years thereafter 10,300    
Change in Assumptions for Defined Benefit Plans      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) $ 1,800