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Derivative Instruments and Hedging Activities (Derivative Positions and Settlements) (Details) (Commodity Contract [Member])
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Jun. 30, 2012
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Designated as Hedging Instrument [Member] | Crude Oil [Member] | Average Floor Price per Hedge of $90 and Average Ceiling Price per Hedge of $122 [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Nonmonetary Notional Amount (in Volumes per Month) | 25,000 | [1] | ||||
| Average Ceiling Price per Hedge (in dollars per instrument) | 122.00 | [1] | ||||
| Average Floor Price per Hedge (in dollars per instrument) | 90.00 | [1] | ||||
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Designated as Hedging Instrument [Member] | Crude Oil [Member] | Average Floor Price per Hedge of $95 and Average Ceiling Price per Hedge of $125 [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Nonmonetary Notional Amount (in Volumes per Month) | 25,000 | [1] | ||||
| Average Ceiling Price per Hedge (in dollars per instrument) | 125.00 | [1] | ||||
| Average Floor Price per Hedge (in dollars per instrument) | 95.00 | [1] | ||||
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Not Designated as Hedging Instrument [Member] | Crude Oil [Member] | Average Floor Price per Hedge of $90 and Average Ceiling Price per Hedge of $116 [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Nonmonetary Notional Amount (in Volumes per Month) | 40,000 | [1] | ||||
| Average Ceiling Price per Hedge (in dollars per instrument) | 116.00 | [1] | ||||
| Average Floor Price per Hedge (in dollars per instrument) | 90.00 | [1] | ||||
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Not Designated as Hedging Instrument [Member] | Natural gas [Member] | Average Floor Price per Instrument of $3.52 and Average Ceiling Price per of $3.52 Intruments [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Nonmonetary Notional Amount (in Volumes per Month) | 1,371 | |||||
| Average Ceiling Price per Hedge (in dollars per instrument) | 3.52 | [2] | ||||
| Average Floor Price per Hedge (in dollars per instrument) | 3.52 | [2] | ||||
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Not Designated as Hedging Instrument [Member] | Natural gas [Member] | Average Floor Price per Instrument of $3.00 [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Nonmonetary Notional Amount (in Volumes per Month) | 91,000 | [2] | ||||
| Average Floor Price per Hedge (in dollars per instrument) | 3.00 | [2] | ||||
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Not Designated as Hedging Instrument [Member] | Natural gas [Member] | Average Ceiling Price per Instrument of $4.75 [Member]
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| Derivative [Line Items] | ||||||
| Derivative, Nonmonetary Notional Amount (in Volumes per Month) | 38,000 | [2] | ||||
| Average Ceiling Price per Hedge (in dollars per instrument) | 4.75 | [2] | ||||
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