Pension and Postretirement Benefits (Change in Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Postretirement Medical Benefits
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax [Abstract]
Balance —	$ (163)	$ 1,179
Amortization of net loss	(172)	(223)
Amortization of prior service cost	76	77
Net gain (loss) arising during the year	1,139	(1,196)
Prior service (cost) benefit arising during the year	(122)	(122)	$ (122)
Balance —	880	(163)	1,179
Domestic Plan
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax [Abstract]
Balance —	(69,132)	(61,647)
Amortization of net loss	3,766	3,136
Amortization of prior service cost	70	306
Net gain (loss) arising during the year	16,009	(11,618)
Settlement (gain) loss	(135)	57
Prior service (cost) benefit arising during the year	(368)	634
Balance —	(49,790)	(69,132)	(61,647)
Foreign Plan
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax [Abstract]
Balance —	(68,260)	(59,993)
Amortization of net loss	2,756	3,673
Net gain (loss) arising during the year	2,289	(20,071)
Settlement loss	1,668	610
Prior service benefit arising during the year	28	0
Currency translation impact and other	(6,353)	7,521
Prior service (cost) benefit arising during the year	4	(4)	12
Balance —	$ (67,872)	$ (68,260)	$ (59,993)