Pensions and Other Post-retirement Benefits - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Period of amortization for actuarial gains and losses	11 years
Estimated contributions by employer to pension plans	$ 5,900
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	6.00%
Percentage of change in assumed health care cost trend rate	1.00%
Increase or decrease in other postretirement obligations	$ 810
Increase or decrease in current year plan expense	55
Defined contribution pension plan expense	5,100	$ 6,800	$ 6,500
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Estimated benefit payments, 2017	20,900
Estimated benefit payments, 2018	21,600
Estimated benefit payments, 2019	22,200
Estimated benefit payments, 2020	23,700
Estimated benefit payments, 2021	24,600
Estimated benefit payments, five years thereafter	138,500
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Estimated benefit payments, 2017	1,700
Estimated benefit payments, 2018	1,700
Estimated benefit payments, 2019	1,900
Estimated benefit payments, 2020	1,800
Estimated benefit payments, 2021	1,900
Estimated benefit payments, five years thereafter	$ 8,100