Acquired Proved Reserves by Type of Reserve, Percentage

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- Definition

The amount of Accounts Payable recognized as of the acquisition date.

+ Details

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- Definition

The amount of Accounts Receivable recognized as of the acquisition date.

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- Definition

The amount of Asset Retirement Obligation recognized as of the acquisition date.

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- Definition

The Net amount recognized as of the acquisition date for the aggregate identifiable assets acquired in excess of or less than the aggregate liabilities assumed.

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- Definition

Oil and Gas Property Acquisition, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net [Abstract]

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- Definition

The amount of Proved Properties recognized as of the acquisition date.

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- Definition

The amount of Unproved Properties assumed at the acquisition date.

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- Definition

Percentage of Undeveloped Portion of Proved Reserves

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- Definition

Significant Acquisitions and Disposals, Estimated Purchase Price

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- Definition

Undeveloped acreage is considered to be those lease acres on which wells have not been drilled or completed to a point that would permit the production of commercial quantities of oil and gas regardless of whether or not such acreage contains proved reserves. Net acres is the sum of the fractional interest owned based on working interests or other economic arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Industry Guide

-Number 2

-Paragraph 5

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The net result for the period of deducting operating expenses from operating revenues.

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- Definition

The net quantity of proved reserves as of the balance sheet date. Proved oil reserves are the estimated quantities of crude oil and natural gas liquids which geological and engineering data demonstrate with reasonable certainty to be recoverable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-10.(a)(2))

-URI http://asc.fasb.org/extlink&oid=6949603&loc=d3e511914-122862

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 19

-Paragraph 59F

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 4

-Section 10

-Paragraph a

-Subparagraph 2

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 235

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6821537&loc=d3e61831-109447

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Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 5

-Section 03

-Paragraph 1

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=6880815&loc=d3e20235-122688

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- Definition

The value of all consideration given or received by the Entity in the significant acquisition or disposal.

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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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Acquisition and Dispositions of Oil and Gas Properties (Details) (USD $)	3 Months Ended		9 Months Ended		3 Months Ended										1 Months Ended	9 Months Ended		1 Months Ended				1 Months Ended	9 Months Ended	1 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 Purchase and Sale Agreement October 2011, Permian Basin, First Acquisition MMBoe	Sep. 30, 2011 Purchase and Sale Agreement October 2011, Permian Basin, First Acquisition Oil Reserves	Sep. 30, 2011 Purchase and Sale Agreement October 2011, Permian Basin, First Acquisition Natural Gas Liquids Reserves	Sep. 30, 2011 Purchase and Sale Agreement October 2011, Permian Basin, First Acquisition Natural Gas Reserves	Sep. 30, 2011 Purchase and Sale Agreement October 2011, Permian Basin, Second Acquisition MMBoe	Sep. 30, 2011 Purchase and Sale Agreement October 2011, Permian Basin, Second Acquisition Oil Reserves	Sep. 30, 2011 Purchase and Sale Agreement October 2011, Permian Basin, Second Acquisition Natural Gas Liquids Reserves	Sep. 30, 2011 Purchase and Sale Agreement October 2011, Permian Basin, Second Acquisition Natural Gas Reserves	Jul. 31, 2011 July 2011, Permian Basin	Apr. 30, 2011 April 2011, Permian Basin A	Dec. 31, 2010 Dec 15, 2010, Permian Basin	Sep. 30, 2011 Dec 15, 2010, Permian Basin	Dec. 15, 2010 Dec 15, 2010, Permian Basin MMBoe	Dec. 31, 2010 Dec 15, 2010, Permian Basin Oil Reserves	Dec. 31, 2010 Dec 15, 2010, Permian Basin Natural Gas Liquids Reserves	Dec. 31, 2010 Dec 15, 2010, Permian Basin Natural Gas Reserves	Dec. 09, 2010 Dec 9, 2010, Permian Basin Boe	Sep. 30, 2010 Sep 30, 2010, Permian Basin MMBoe	Sep. 30, 2011 Sep 30, 2010, Permian Basin	Sep. 30, 2010 Sep 30, 2010, Permian Basin Oil Reserves	Sep. 30, 2010 Sep 30, 2010, Permian Basin Natural Gas Liquids Reserves	Sep. 30, 2010 Sep 30, 2010, Permian Basin Natural Gas Reserves
Significant Acquisitions and Disposals [Line Items]
Consideration - Estimated Purchase Price					$ 158,000,000				$ 54,000,000
Consideration - Purchase Price													22,000,000	37,000,000			73,630,000				103,000,000	188,314,000
Gas and Oil Acreage, Undeveloped, Net														11,000
Proved Developed and Undeveloped Reserves, Net					13.8				3.4								7.6				0	18
Percentage of Undeveloped Portion of Proved Reserves					76.00%				77.00%						92.00%							89.00%
Acquired Proved Reserves by Type of Reserve, Percentage						59.00%	25.00%	16.00%		61.00%	24.00%	15.00%						62.00%	24.00%	14.00%				65.00%	22.00%	13.00%
Recognized amounts of identifiable assets acquired and liabilities assumed
Proved properties																	41,066,000					151,747,000
Unproved leasehold properties																	32,500,000					35,360,000
Accounts receivable																	143,000					1,461,000
Asset retirement obligation																	(79,000)					(142,000)
Accounts payable																						(112,000)
Total identifiable net assets																	73,630,000					188,314,000
Operating revenues	378,568,000	295,804,000	1,195,331,000	1,204,443,000												6,800,000							32,800,000
Operating income	$ 150,412,000	$ 67,320,000	$ 416,628,000	$ 357,811,000												$ 3,200,000							$ 16,200,000