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Fair Value Measurements (Hierarchy Of Fair Value, Assets And Liabilities Measured On Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2012 | Dec. 31, 2011
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets (liabilities) | $ 178,207 | $ 245,369
Commodity Derivative Instruments [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets (liabilities) | (22,345) | (5,050)
Money Market Funds [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets (liabilities) | 200,552 | 250,419
Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets (liabilities) | 200,552 | 250,419
Fair Value, Inputs, Level 1 [Member] | Commodity Derivative Instruments [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets (liabilities) |  |
Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets (liabilities) | 200,552 | 250,419
Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets (liabilities) | (22,345) |
Fair Value, Inputs, Level 2 [Member] | Commodity Derivative Instruments [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets (liabilities) | (22,345) |
Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets (liabilities) |  |
Fair Value, Inputs, Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets (liabilities) |  | (5,050)
Fair Value, Inputs, Level 3 [Member] | Commodity Derivative Instruments [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets (liabilities) |  | (5,050)
Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets (liabilities) |  |

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- Definition This element represents the aggregate of the assets reported on the balance sheet at period end measured at fair value by the entity. This element is intended to be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. + References No definition available. + Details
Name: | us-gaap_AssetsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration