Derivatives Commodity Instruments - Cash Flow Hedging Relationship in Financial Statements (Details) - Commodity contracts - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net gain recognized in other comprehensive income on derivatives (effective portion), net of tax		$ 9		$ 11
Unrealized gain (loss) on derivatives arising during period, tax	$ 0	6	$ 0	7
Gain (loss) on derivative instruments, net
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain reclassified from accumulated other comprehensive income into income (effective portion)		$ 5,735		$ 9,789

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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

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-Publisher FASB

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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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Amount of tax expense (benefit), before reclassification adjustments, related to 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).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

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-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e640-108580

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

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-Paragraph 10A

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-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580

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