Subsequent Event (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended
Oct. 31, 2011	Sep. 30, 2011
Consol Energy Inc [Member]
Subsequent Event [Line Items]
Percentage of interest in acres acquired from Consol Energy Inc.	50.00%
Acreage acquired from Consol Energy Inc (In acres)	200,000
Cash paid for percentage of interest in acres acquired	$ 59
Total drilling costs payable over five year period (maximum)	534
Years to pay the drilling costs	5 years
Drilling carry percentage share	50.00%
South Arne Field [Member]
Subsequent Event [Line Items]
Acquisition of additional interests in oil and gas fields	4.00%
New percentage interest in South Arne Field	62.00%
Prior percentage interest in South Arne Field		58.00%
Purchase price for acquisition of additional interests in oil and gas fields	$ 116

Acquisition of additional interests in oil and gas fields.

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- Definition

Acreage acquired from Consol Energy Inc.

+ Details

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- Definition

Cash paid for percentage of interest in acres acquired from Consol Energy Inc.

+ Details

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- Definition

Drilling carry percentage share.

+ Details

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- Definition

Total drilling costs payable over a five year period (maximum).

+ Details

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- Definition

New percentage interest in south Arne field after acquisition.

+ Details

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- Definition

Percentage of undivided interest in acres acquired from Consol Energy Inc.

+ Details

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- Definition

Prior percentage interest in south Arne field before acquisition.

+ Details

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- Definition

Purchase price for acquisition of additional interests in South Arne field.

+ Details

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- Definition

The number of years to pay the drilling costs.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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