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Supplemental Information on Oil and Natural Gas Producing Activities - Summary of Changes in Estimated Oil and Natural Gas Reserves (Unaudited) (Details)
12 Months Ended
Dec. 31, 2014
MBbls
Dec. 31, 2013
MBbls
Dec. 31, 2012
MBbls
Dec. 31, 2011
MBbls
Oil Reserves        
Proved Developed and Undeveloped Reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas)        
Proved developed and undeveloped reserves, beginning balance 142,641us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
[1] 262,045us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
[1] 214,450us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
 
Revisions of previous estimates (18,687)us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
(13,969)us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
(37,394)us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
 
Acquisitions of new reserves 1,009us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
43us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
31,470us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
 
Extensions and discoveries 37,603us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
40,570us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
89,656us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
 
Sales of reserves in place (25,659)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
(131,769)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
(20,269)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
 
Production (10,876)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
(14,279)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
(15,868)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
 
Proved developed and undeveloped reserves, ending balance 126,031us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
[1] 142,641us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
[1] 262,045us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
[1]  
Proved developed reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 79,022us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
83,893us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
136,605us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
101,578us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
Proved undeveloped reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 47,009us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
58,748us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
125,440us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
112,872us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
Natural Gas Liquids        
Proved Developed and Undeveloped Reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas)        
Proved developed and undeveloped reserves, beginning balance 59,052us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
[1] 67,994us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
[1] 30,335us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
 
Revisions of previous estimates 11,103us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
3,717us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
15,098us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
 
Acquisitions of new reserves 441us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
13us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
683us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
 
Extensions and discoveries 27,500us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
18,686us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
27,259us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
 
Sales of reserves in place (2,516)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
(29,067)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
(3,287)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
 
Production (3,794)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
(2,291)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
(2,094)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
 
Proved developed and undeveloped reserves, ending balance 91,786us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
[1] 59,052us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
[1] 67,994us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
[1]  
Proved developed reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 56,823us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
35,807us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
33,785us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
17,150us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
Proved undeveloped reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 34,963us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
23,245us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
34,209us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
13,185us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
Natural Gas        
Proved Developed and Undeveloped Reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas)        
Proved developed and undeveloped reserves, beginning balance 1,390,429us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[1],[2] 1,415,042us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[1],[2] 1,355,056us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2]  
Revisions of previous estimates 167,589us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] (53,432)us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] (538,214)us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2]  
Acquisitions of new reserves 12,527us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] 363us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] 202,995us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2]  
Extensions and discoveries 467,185us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] 359,918us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] 489,302us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2]  
Sales of reserves in place (163,800)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] (228,229)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] (548)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2]  
Production (85,697)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] (103,233)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] (93,549)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2]  
Proved developed and undeveloped reserves, ending balance 1,788,233us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[1],[2] 1,390,429us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[1],[2] 1,415,042us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[1],[2]  
Proved developed reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 1,203,447us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] 951,609us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] 896,701us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] 670,382us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2]
Proved undeveloped reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 584,786us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] 438,820us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] 518,341us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2] 684,674us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2]
[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.