Health Care, Pension and Other Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Postretirement Benefits Other than Pensions
Net periodic benefit cost:
Service cost	$ 498	$ 543
Interest cost	2,545	2,643
Recognition of:
Unrecognized prior service cost	(1,642)	(1,645)
Unrecognized actuarial loss	581	11
Ongoing pension (credit) cost	1,982	1,552
Curtailment expense
Net pension costs (credits)	1,982	1,552
Domestic Defined Benefit Pension Plans | Defined Benefit Pension Plans
Net periodic benefit cost:
Service cost	4,357	5,313
Interest cost	8,152	6,410
Expected return on assets	(14,434)	(10,309)
Recognition of:
Unrecognized prior service cost	379	341
Unrecognized actuarial loss		1,661
Ongoing pension (credit) cost	(1,546)	3,416
Curtailment expense	(825)
Net pension costs (credits)	(721)	3,416
Foreign Defined Benefit Pension Plans | Defined Benefit Pension Plans
Net periodic benefit cost:
Service cost	2,016	1,918
Interest cost	2,352	1,638
Expected return on assets	(2,685)	(1,764)
Recognition of:
Unrecognized prior service cost	0
Unrecognized actuarial loss	383	(53)
Ongoing pension (credit) cost	2,066	1,739
Curtailment expense	0
Net pension costs (credits)	$ 2,066	$ 1,739