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Derivative Instruments and Hedging Activities (Derivative Positions and Settlements) (Details) (Not Designated as Hedging Instrument [Member], Commodity Contract [Member])
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Jun. 30, 2013
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Natural gas [Member] | Fixed-Price Swap per Instrument of 3 Point 52 Dollars [Member]
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| Derivative [Line Items] | |
| Average Notional Volumes per Month | 91,000 |
| Fixed-Price Swap | 3.52 |
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Natural gas [Member] | Average Floor Price per Instrument of $3.00 [Member]
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| Derivative [Line Items] | |
| Average Notional Volumes per Month | 91,000 |
| Put/Call Price | 3.00 |
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Natural gas [Member] | Average Ceiling Price per Instrument of $4.75 [Member]
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| Derivative [Line Items] | |
| Average Notional Volumes per Month | 38,000 |
| Put/Call Price | 4.75 |
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Crude Oil [Member] | Derivative Average Floor Price per Instrument of 101 Point 30 Dollars and Average Ceiling Price per Instrument of 101 Point 30 Dollars [Member]
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| Derivative [Line Items] | |
| Average Notional Volumes per Month | 40,000 |
| Fixed-Price Swap | 101.30 |
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Crude Oil [Member] | Derivative Average Floor Price per Instrument of 93 Point 35 Dollars and Average Ceiling Price per Instrument of 93 Point 35 Dollars [Member]
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| Derivative [Line Items] | |
| Average Notional Volumes per Month | 30,000 |
| Fixed-Price Swap | 93.35 |
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Crude Oil [Member] | Average Floor Price per Instrument of $70 [Member]
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| Derivative [Line Items] | |
| Average Notional Volumes per Month | 30,000 |
| Put/Call Price | 70.00 |