The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4D
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624177-113959

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- Definition

The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

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- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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Derivatives Derivatives (Summary of gains (losses) recognized in Statement of Operations and AOCI) (Details) - Cash Flow Hedging - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Designated as Hedging Instrument
Derivative [Line Items]
Effective portion of derivative gain (loss) reclassified from accumulated other comprehensive loss into income (loss)	$ 4	$ (382)	$ (337)	$ (900)
Not Designated as Hedging Instrument
Derivative [Line Items]
Gain (loss) on contracts where hedge accounting was not elected	0	(236)	0	(819)
Other Comprehensive Income (Loss) \| Designated as Hedging Instrument
Derivative [Line Items]
Effective portion of derivative gain (loss) recognized in other comprehensive income (loss)	603	(858)	2,067	(1,124)
Other Comprehensive Income (Loss) \| Designated as Hedging Instrument \| Natural Gas Contracts
Derivative [Line Items]
Effective portion of derivative gain (loss) recognized in other comprehensive income (loss)	123	(239)	334	(709)
Other Comprehensive Income (Loss) \| Designated as Hedging Instrument \| Interest Rate Swap
Derivative [Line Items]
Effective portion of derivative gain (loss) recognized in other comprehensive income (loss)	480	(619)	1,733	(415)
Cost of Sales \| Designated as Hedging Instrument \| Natural Gas Contracts
Derivative [Line Items]
Effective portion of derivative gain (loss) reclassified from accumulated other comprehensive loss into income (loss)	(36)	90	(234)	157
Interest Expense \| Designated as Hedging Instrument \| Interest Rate Swap
Derivative [Line Items]
Effective portion of derivative gain (loss) reclassified from accumulated other comprehensive loss into income (loss)	40	(472)	(103)	(1,057)
Other Non-Operating Income (Expense) \| Not Designated as Hedging Instrument \| Natural Gas Contracts
Derivative [Line Items]
Gain (loss) on contracts where hedge accounting was not elected	$ 0	$ (236)	$ 0	$ (819)