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		9 Months Ended			12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Settlements, Benefit Obligation				$ 3,500
Defined Benefit Plan, Service Cost						$ 1,800
Net periodic cost						5,300
Pension Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Settlements, Benefit Obligation	$ 0	$ 3,482	$ 0	3,482
Defined Benefit Plan, Service Cost	518	391	1,552	1,171
Interest cost	3,288	3,518	9,862	10,779
Expected return on plan assets	(4,691)	(4,847)	(14,073)	(14,608)
Amortization of prior service cost (credit)	2	6	6	17
Amortization of actuarial loss	2,468	2,865	7,405	8,510
Net periodic cost	1,585	5,415	4,752	9,351
Other Postretirement Employee Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Settlements, Benefit Obligation			0	0	$ 0	$ 0
Defined Benefit Plan, Service Cost	41	62	122	187
Interest cost	688	730	2,059	2,306
Expected return on plan assets	0	0	(1)	(1)
Amortization of prior service cost (credit)	(384)	(428)	(1,151)	(1,284)
Amortization of actuarial loss	(1,662)	(2,233)	(4,963)	(5,674)
Net periodic cost	(1,317)	(1,869)	(3,934)	(4,466)
Selling, General and Administrative Expenses [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax	100	100	300	600
Defined Benefit Plan, Settlements, Benefit Obligation				1,600
Cost of Sales [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax	$ 200	$ 100	$ 500	800
Defined Benefit Plan, Settlements, Benefit Obligation				$ 1,900