Accumulated Other Comprehensive Income (Loss) (Schedule of AOCI) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2017
Change in Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance				$ (114,405)
Cumulative-effect adjustment for the adoption of ASU 2017-12						$ 0
Ending balance		$ (120,299)		(120,299)
Foreign Currency Translation
Change in Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance		(23,266)	$ (11,850)	(23,240)	$ (16,183)
Cumulative-effect adjustment for the adoption of ASU 2017-12						0
Amounts recognized into AOCI		(533)	(7,392)	(289)	(3,059)
Currency impact		0	0	0	0
Amounts reclassified from AOCI, Currency		0	0	0	0
Tax effect		262	0	(8)	0
Other comprehensive income (loss), net of tax		(271)	(7,392)	(297)	(3,059)
Ending balance		(23,537)	(19,242)	(23,537)	(19,242)
Derivative Instruments
Change in Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance		(5,920)	1,546	(2,866)	351
Cumulative-effect adjustment for the adoption of ASU 2017-12						(275)
Amounts recognized into AOCI		(6,093)	603	(9,608)	2,067
Currency impact		0	0	0	0
Amounts reclassified from AOCI, Derivatives	[1]	(270)	(4)	(753)	337
Tax effect		1,533	(127)	2,477	(462)
Other comprehensive income (loss), net of tax		(4,830)	472	(7,884)	1,942
Ending balance		(10,750)	2,018	(10,750)	2,018
Pension and Other Post-retirement Benefits
Change in Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance		(87,522)	(88,585)	(88,299)	(89,340)
Cumulative-effect adjustment for the adoption of ASU 2017-12						0
Amounts recognized into AOCI		1,148	1,527	1,148	1,527
Currency impact		(84)	524	(50)	40
Amounts reclassified from AOCI, Pension/PRW	[2]	945	1,564	1,915	3,170
Tax effect		(499)	(736)	(726)	(1,103)
Other comprehensive income (loss), net of tax		1,510	2,879	2,287	3,634
Ending balance		(86,012)	(85,706)	(86,012)	(85,706)
Accumulated Other Comprehensive Loss
Change in Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance		(116,708)	(98,889)	(114,405)	(105,172)
Cumulative-effect adjustment for the adoption of ASU 2017-12						$ (275)
Amounts recognized into AOCI		(5,478)	(5,262)	(8,749)	535
Currency impact		(84)	524	(50)	40
Amounts reclassified from AOCI		675	1,560	1,162	3,507
Tax effect		1,296	(863)	1,743	(1,565)
Other comprehensive income (loss), net of tax		(3,591)	(4,041)	(5,894)	2,517
Ending balance		$ (120,299)	$ (102,930)	$ (120,299)	$ (102,930)

[1] We reclassified natural gas contracts through cost of sales and the interest rate swaps through interest expense on the Condensed Consolidated Statements of Operations. See note 8 for additional information.

[2] We reclassified the net pension and non-pension post-retirement benefits amortization and settlement charges through other income (expense) on the Condensed Consolidated Statements of Operations. See note 6 for additional information.