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Supplemental Information on Oil and Natural Gas Producing Activities - Summary of Changes in Estimated Oil and Natural Gas Reserves - Noncontrolling Interests (Unaudited) (Additional Information) (Details) | Dec. 31, 2014 MBbls | Dec. 31, 2013 MBbls | Dec. 31, 2012 MBbls | Dec. 31, 2011 MBbls
--- | --- | --- | --- | ---
Oil Reserves |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) | 126,031 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember | [1] | 142,641 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember | [1] | 262,045 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember | [1] | 214,450 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember |
Natural Gas Liquids |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) | 91,786 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember | [1] | 59,052 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember | [1] | 67,994 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember | [1] | 30,335 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember |
Natural Gas Reserves |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) | 1,788,233 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember | [1],[2] | 1,390,429 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember | [1],[2] | 1,415,042 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember | [1],[2] | 1,355,056 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember | [2]
Non-controlling Interest | Oil Reserves |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) | 11,027 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember / us-gaap_StatementEquityComponentsAxis = us-gaap_NoncontrollingInterestMember |  | 13,569 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember / us-gaap_StatementEquityComponentsAxis = us-gaap_NoncontrollingInterestMember |  | 17,340 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_OilReservesMember / us-gaap_StatementEquityComponentsAxis = us-gaap_NoncontrollingInterestMember |  |  |
Non-controlling Interest | Natural Gas Liquids |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) | 4,761 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember / us-gaap_StatementEquityComponentsAxis = us-gaap_NoncontrollingInterestMember |  | 4,737 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember / us-gaap_StatementEquityComponentsAxis = us-gaap_NoncontrollingInterestMember |  | 5,132 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasLiquidsReservesMember / us-gaap_StatementEquityComponentsAxis = us-gaap_NoncontrollingInterestMember |  |  |
Non-controlling Interest | Natural Gas Reserves |  |  |  |  |  |  |  |
Reserve Quantities [Line Items] |  |  |  |  |  |  |  |
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) | 70,833 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember / us-gaap_StatementEquityComponentsAxis = us-gaap_NoncontrollingInterestMember |  | 69,693 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember / us-gaap_StatementEquityComponentsAxis = us-gaap_NoncontrollingInterestMember |  | 94,543 us-gaap_ProvedDevelopedAndUndevelopedReservesNet / us-gaap_ReserveQuantitiesByTypeOfReserveAxis = us-gaap_NaturalGasReservesMember / us-gaap_StatementEquityComponentsAxis = us-gaap_NoncontrollingInterestMember |  |  |
[1] | Includes proved reserves attributable to noncontrolling interests at December 31, 2014, 2013 and 2012 as shown in the table below: December 31, 2014 2013 2012Oil (MBbl)11,027 13,569 17,340NGL (MBbl)4,761 4,737 5,132Natural gas (MMcf)70,833 69,693 94,543
[2] | 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 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 2: 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=27015464&loc=d3e511914-122862 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 10 -Paragraph a -Subparagraph 2 -Article 4 + Details
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