Pension and Other Postretirement Employee Benefit Plans Components of Net Periodic Cost of Pension and Other Postretirement Employee Benefit Plans (Detail 2) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	$ 434	$ 560
Interest cost	3,000	3,278
Expected return on plan assets	(4,254)	(4,694)
Amortization of prior service cost (credit)	0	2
Amortization of actuarial loss	2,570	2,525
Net periodic cost	1,750	1,671
Other Postretirement Employee Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	48	68
Interest cost	607	704
Expected return on plan assets	0	0
Amortization of prior service cost (credit)	(419)	(383)
Amortization of actuarial loss	(225)	(1,480)
Net periodic cost	11	(1,091)
Selling, General and Administrative Expenses [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	200	(100)
Cost of Sales [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	$ 300	$ 400