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Derivative Commodity Instruments (Fair Values Of Derivative Instruments In Consolidated Balance Sheets) (Details) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2011 | Dec. 31, 2010
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Derivative [Line Items] |  |
Total asset derivatives | $ 2,437 | $ 47
Total liability derivatives | 4,235 | 46
Accounts Receivable, Net [Member] | Commodity Forward Contracts [Member] |  |
Derivative [Line Items] |  |
Derivatives Not Designated as Hedging Instruments, Asset Derivatives | 2,437 | 47
Accrued Liabilities [Member] | Commodity Forward Contracts [Member] |  |
Derivative [Line Items] |  |
Derivatives Designated as Hedging Instruments, Liability Derivatives | 3,262 |
Derivatives Not Designated as Hedging Instruments, Liability Derivatives | $ 973 | $ 46

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