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Derivative Financial Instruments Derivative Financial Instruments (Schedule of Derivative Offset Amounts) (Details) (Exchange Traded [Member], USD $)
In Thousands, unless otherwise specified |
Dec. 31, 2013
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Dec. 31, 2012
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| Derivative [Line Items] | |||||
| Derivative Liability, Fair Value, Gross Liability | $ (7,167) | $ (9,388) | |||
| Derivative Asset, Fair Value, Gross Asset | 2,665 | 2,050 | |||
| Derivative Liability, Fair Value, Amount Not Offset Against Collateral | 4,502 | [1] | 7,338 | ||
| Derivative Liability, Fair Value of Collateral | 14,782 | 18,304 | |||
| Margin Deposit Net of Commodity Contract | 10,280 | 10,966 | |||
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Other Current Liabilities [Member]
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| Derivative [Line Items] | |||||
| Derivative Liability, Fair Value, Amount Not Offset Against Collateral | 6,737 | ||||
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Other Noncurrent Assets [Member]
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| Derivative [Line Items] | |||||
| Derivative Liability, Fair Value, Amount Not Offset Against Collateral | $ (2,235) | ||||
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