Accumulated Other Comprehensive Income (Loss) - Reclassifications of Accumulated Other Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Gains (losses) on cash flow hedges:
Income tax expense	$ 8,701us-gaap_IncomeTaxExpenseBenefit	$ (8,248)us-gaap_IncomeTaxExpenseBenefit
Reclassification out of Accumulated Other Comprehensive Income
Gains (losses) on cash flow hedges:
Net of tax	(1,851)	(3,389)
Cash Flow Hedges \| Reclassification out of Accumulated Other Comprehensive Income
Gains (losses) on cash flow hedges:
Total	0	3,608
Income tax expense	0	(1,384)
Net of tax	0	2,224
Pension and Postretirement Plans \| Reclassification out of Accumulated Other Comprehensive Income
Gains (losses) on cash flow hedges:
Total	(2,847)	(8,636)
Income tax expense	996	3,023
Net of tax	(1,851)	(5,613)
Pension and postretirement plans:
Transition obligation	0	(10)
Prior service cost	0	(74)
Actuarial losses	(2,847)	(8,552)
Commodity contracts \| Cash Flow Hedges \| Reclassification out of Accumulated Other Comprehensive Income
Gains (losses) on cash flow hedges:
Reclassification Adjustment from AOCI on Derivatives	0	4,054
Interest rate swap \| Cash Flow Hedges \| Reclassification out of Accumulated Other Comprehensive Income
Gains (losses) on cash flow hedges:
Reclassification Adjustment from AOCI on Derivatives	$ 0	$ (446)

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This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses and taxes from ongoing operations before extraordinary items, and noncontrolling interest.

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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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Net income after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).

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Amount before tax of reclassification adjustment from accumulated other comprehensive (income) loss for prior service cost (credit) related to pension and other postretirement benefit plans.

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Amount before tax of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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