Derivative Instruments and Hedging Activities (Derivative Positions and Subsequent Event) (Details) (Commodity Contract [Member])
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Dec. 31, 2012
Crude Oil [Member]
Average Floor Price per Hedge of $90 and Average Ceiling Price per Hedge of $116 [Member]
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Dec. 31, 2012
Natural gas [Member]
Option
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Dec. 31, 2012
Natural gas [Member]
Fixed-Price Swap per Instrument of $3.52 [Member]
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Dec. 31, 2012
Natural gas [Member]
Average Floor Price per Instrument of $3.00 [Member]
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Dec. 31, 2012
Natural gas [Member]
Average Ceiling Price per Instrument of $4.75 [Member]
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Jan. 31, 2013
Subsequent Event [Member]
Crude Oil [Member]
Derivative Average Floor Price per Instrument of $101.30 and Average Ceiling Price per Instrument of $101.30 [Member]
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Jan. 31, 2013
Subsequent Event [Member]
Crude Oil [Member]
Derivative Average Floor Price per Instrument of $93.35 and Average Ceiling Price per Instrument of $93.35 [Member]
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Jan. 31, 2013
Subsequent Event [Member]
Crude Oil [Member]
Average Floor Price per Instrument of $70.00 [Member]
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Derivative [Line Items] | ||||||||||||||||||||||
Number of options sold (in options) | 2 | |||||||||||||||||||||
Derivative, Nonmonetary Notional Amount (in Volumes per Month) | 40,000 | [1],[2] | 91,000 | [3] | 91,000 | [3] | 38,000 | [3] | 40,000 | [4] | 30,000 | 30,000 | [4] | |||||||||
Derivative, Average Cap Price | 116.00 | [1],[2] | 3.52 | [3] | 101.30 | [4] | 93.35 | 70.00 | [4] | |||||||||||||
Average Ceiling Price per Hedge (in dollars per instrument) | 90.00 | [1],[2] | 3.00 | [3] | 4.75 | [3] | ||||||||||||||||
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