Retirement Plans and Postretirement Medical Benefits (Pretax Amounts Recognized in AOCI) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Nonpension postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 43,160	$ 41,625
Prior service credit	1,466	1,763
Total	44,626	43,388
United States | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	835,265	873,523
Prior service credit	(391)	(452)
Transition asset	0	0
Total	834,874	873,071
Foreign | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	321,914	342,169
Prior service credit	(597)	(667)
Transition asset	(24)	(32)
Total	$ 321,293	$ 341,470