Pensions and Other Post-retirement Benefits - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Estimated contributions by employer to pension plans		$ 5,000
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%
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		$ 760
Increase or decrease in current year plan expense		100
Defined contribution pension plan expense		$ 8,100	$ 5,100	$ 6,800
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)		$ 18,526	6,332	11,955
Service cost		11,023	10,417	11,517
Estimated benefit payments, year one		23,600
Estimated benefit payments, year two		23,800
Estimated benefit payments, year three		24,900
Estimated benefit payments, year four		25,800
Estimated benefit payments, year five		26,500
Estimated benefit payments, five years thereafter		146,800
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)		516	1,021	999
Service cost		403	$ 426	$ 444
Estimated benefit payments, year one		1,600
Estimated benefit payments, year two		1,700
Estimated benefit payments, year three		1,700
Estimated benefit payments, year four		1,800
Estimated benefit payments, year five		1,800
Estimated benefit payments, five years thereafter		$ 7,400
Scenario, Forecast | Change in Assumptions for Defined Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 1,800