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Supplemental Information on Oil and Natural Gas Producing Activities - Summary of Changes in Estimated Oil and Natural Gas Reserves (Unaudited) (Parenthetical) (Details) | Dec. 31, 2012 MMcf | Dec. 31, 2011 MMcf | Dec. 31, 2010 MMcf | Dec. 31, 2009 MMcf
--- | --- | --- | --- | ---
Oil Reserves |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) |  |  | 244,785 | [1] | 252,114 |  | 105,349 |
Natural Gas Liquids |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) | 67,994 | [1],[2] | 30,335 | [1],[2] |  |  |  |
Natural Gas Reserves |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) | 1,415,042 | [1],[3] | 1,355,056 | [1],[3] | 1,762,665 | [3] | 680,075 | [3]
Oil Excluding NGLs |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) | 262,045 |  | 214,450 | [1] |  |  |  |
Noncontrolling Interest | Natural Gas Liquids |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) | 5,132 |  | 1,782 |  |  |  |  |
Noncontrolling Interest | Natural Gas Reserves |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) | 94,543 |  | 45,500 |  |  |  |  |
Noncontrolling Interest | Oil Excluding NGLs |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) | 17,340 |  | 17,018 |  |  |  |  |
[1] | Proved reserves at December 31, 2012 and 2011, respectively, include approximately 17,340 MBbls and 17,018 MBbls of oil, 5,132 MBbls and 1,782 MBbls of NGLs and 94,543 MMcf and 45,500 MMcf of natural gas attributable to noncontrolling interests.
[2] | Prior to 2012, NGLs did not comprise a significant portion of total proved reserves and were included with oil reserves, which affects the comparability of estimated reserves for 2012, 2011 and 2010.
[3] | Natural gas reserves are computed at 14.65 pounds per square inch absolute and 60 degrees Fahrenheit.

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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 SEC -Name Regulation S-X (SX) -Number 210 -Section 10 -Paragraph a -Subparagraph 2 -Article 4 Reference 2: 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=8451039&loc=d3e61831-109447 Reference 3: 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=21918352&loc=d3e511914-122862 Reference 4: 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. + Details
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- Details
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