Accumulated Comprehensive Income (Loss) (Schedule of AOCI) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		$ (125,197)	$ (120,232)	$ (138,447)
Change in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Amounts recognized into AOCI		18,856	(18,307)	(13,834)
Currency impact		(152)	1,271	4,233
Amounts reclassified from AOCI		7,366	8,980	33,669
Tax effect		(6,045)	3,091	(5,853)
Other Comprehensive Income (Loss), Net of Tax		20,025	(4,965)	18,215
Ending balance		(105,172)	(125,197)	(120,232)
Foreign Currency Translation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(27,828)	(22,913)	(9,162)
Change in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Amounts recognized into AOCI		12,835	(6,244)	(13,751)
Currency impact		0	0	0
Amounts reclassified from AOCI, Currency		0	0	0
Tax effect		(1,190)	1,329	0
Other Comprehensive Income (Loss), Net of Tax		11,645	(4,915)	(13,751)
Ending balance		(16,183)	(27,828)	(22,913)
Derivative Instruments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(515)	(1,860)	(625)
Change in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Amounts recognized into AOCI		(286)	(1,335)	(4,287)
Currency impact		0	0	0
Amounts reclassified from AOCI, Derivatives	[1]	1,780	3,528	2,357
Tax effect		(628)	(848)	695
Other Comprehensive Income (Loss), Net of Tax		866	1,345	(1,235)
Ending balance		351	(515)	(1,860)
Pension and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance		(96,854)	(95,459)	(128,660)
Change in Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Amounts recognized into AOCI		6,307	(10,728)	4,204
Currency impact		(152)	1,271	4,233
Amounts reclassified from AOCI, Pension/PRW	[2]	5,586	5,452	31,312
Tax effect		(4,227)	2,610	(6,548)
Other Comprehensive Income (Loss), Net of Tax		7,514	(1,395)	33,201
Ending balance		$ (89,340)	$ (96,854)	$ (95,459)

[1] We reclassified natural gas contracts through cost of sales and the interest rate swap through interest expense on the Consolidated Statements of Operations. See note 12 for additional information.

[2] We reclassified the net pension and non-pension post-retirement benefits amortization and settlement charges through cost of sales and selling, general and administrative expenses on the Consolidated Statements of Operations. See notes 8 and 9 for additional information.