Health Care, Pension and Other Benefits (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Postretirement Benefits Other than Pensions
Net periodic benefit (credit) cost:
Service cost	$ 499	$ 471	$ 997	$ 1,014
Interest cost	2,544	2,593	5,089	5,236
Recognition of:
Unrecognized prior service cost	(1,642)	(1,645)	(3,284)	(3,290)
Unrecognized actuarial loss	582	5	1,163	16
Ongoing pension (credit) cost	1,983	1,424	3,965	2,976
Settlements		(9,332)		(9,332)
Net pension (credit) cost	1,983	(7,908)	3,965	(6,356)
Domestic Defined Benefit Pension Plans | Defined Benefit Pension Plans
Net periodic benefit (credit) cost:
Service cost	1,158	5,459	5,515	10,772
Interest cost	8,540	7,191	16,692	13,601
Expected return on assets	(14,382)	(11,299)	(28,816)	(21,608)
Recognition of:
Unrecognized prior service cost	406	340	785	681
Unrecognized actuarial loss		1,662		3,323
Ongoing pension (credit) cost	(4,278)	3,353	(5,824)	6,769
Settlements			825
Net pension (credit) cost	(4,278)	3,353	(4,999)	6,769
Foreign Defined Benefit Pension Plans | Defined Benefit Pension Plans
Net periodic benefit (credit) cost:
Service cost	2,016	2,287	4,032	4,205
Interest cost	2,351	1,864	4,703	3,502
Expected return on assets	(2,685)	(2,008)	(5,370)	(3,772)
Recognition of:
Unrecognized prior service cost
Unrecognized actuarial loss	383	(97)	766	(150)
Ongoing pension (credit) cost	2,065	2,046	4,131	3,785
Settlements
Net pension (credit) cost	$ 2,065	$ 2,046	$ 4,131	$ 3,785