Pension and Postretirement Benefits (Amounts Recognized in Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Postretirement Medical Benefits
Defined Benefit Plan Disclosure [Line Items]
Amortization of unrecognized prior service (benefit) cost	$ 122	$ 122	$ 122
Unrecognized net loss	1,921	(455)
Unrecognized prior service cost	(1,041)	292
Accumulated other comprehensive loss, net of tax	880	(163)	1,179
Domestic Plan
Defined Benefit Plan Disclosure [Line Items]
Amortization of unrecognized prior service (benefit) cost	368	(634)
Unrecognized net loss	(48,825)	(68,476)
Unrecognized prior service cost	(965)	(656)
Accumulated other comprehensive loss, net of tax	(49,790)	(69,132)	(61,647)
Foreign Plan
Defined Benefit Plan Disclosure [Line Items]
Amortization of unrecognized prior service (benefit) cost	(4)	4	(12)
Unrecognized net loss	(67,886)	(68,194)
Unrecognized prior service cost	14	(66)
Accumulated other comprehensive loss, net of tax	$ (67,872)	$ (68,260)	$ (59,993)