Derivatives (Effective Portion of Derivative Gain Loss) (Details) - Cash Flow Hedging - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of derivative gain (loss) recognized in other comprehensive income (loss)	$ (1,909)	$ (1,392)	$ 777
Effective portion of derivative gain (loss) reclassified from accumulated OCI into income	2,131	573	(57)
Designated as Hedging Instrument \| Natural Gas Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of derivative gain (loss) recognized in other comprehensive income (loss)	(1,909)	(1,392)	777
Designated as Hedging Instrument \| Natural Gas Contracts \| Cost of Sales
Derivative Instruments, Gain (Loss) [Line Items]
Effective portion of derivative gain (loss) reclassified from accumulated OCI into income	2,131	$ 573	$ (57)
Not Designated as Hedging Instrument \| Natural Gas Contracts \| Cost of Sales
Derivative Instruments, Gain (Loss) [Line Items]
Gain on Cash Flow Hedge Ineffectiveness	$ 200

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No definition available.

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- Definition

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

+ References

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=56946850&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=56946850&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.

+ References

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- Definition

The gain recognized in earnings during the reporting period representing the amount of the cash flow hedges' ineffectiveness.

+ References

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