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

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

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Amount before tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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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		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Designated as Hedging Instrument
Derivative [Line Items]
Effective portion of derivative gain (loss) reclassified from accumulated OCI to current earnings	$ 183	$ (434)	$ (154)	$ (1,334)
Not Designated as Hedging Instrument
Derivative [Line Items]
Gain (loss) on contracts where hedge accounting was not elected	0	(4)	0	(823)
Other Comprehensive Income (Loss) \| Designated as Hedging Instrument
Derivative [Line Items]
Effective portion of derivative gain (loss) recognized into OCI	(819)	93	1,248	(1,031)
Other Comprehensive Income (Loss) \| Designated as Hedging Instrument \| Natural Gas Contracts
Derivative [Line Items]
Effective portion of derivative gain (loss) recognized into OCI	179	6	513	(703)
Other Comprehensive Income (Loss) \| Designated as Hedging Instrument \| Interest Rate Swaps
Derivative [Line Items]
Effective portion of derivative gain (loss) recognized into OCI	(998)	87	735	(328)
Cost of Sales \| Designated as Hedging Instrument \| Natural Gas Contracts
Derivative [Line Items]
Effective portion of derivative gain (loss) reclassified from accumulated OCI to current earnings	48	(76)	(186)	81
Interest Expense \| Designated as Hedging Instrument \| Interest Rate Swaps
Derivative [Line Items]
Effective portion of derivative gain (loss) reclassified from accumulated OCI to current earnings	135	(358)	32	(1,415)
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	$ (4)	$ 0	$ (823)