Retirement Plans and Postretirement Medical Benefits (Estimated Amounts to be Amortized from AOCI into Net Periodic Benefit) (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Nonpension postretirement benefit plans
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ 3,736
Prior service credit	351
Total	4,087
United States | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	32,303
Prior service credit	(60)
Transition asset	0
Total	32,243
Foreign | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	7,304
Prior service credit	(72)
Transition asset	(7)
Total	$ 7,225