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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, 2013
MBbls
Dec. 31, 2012
MBbls
Dec. 31, 2011
MBbls
Dec. 31, 2010
MBbls
Oil Reserves        
Proved Developed and Undeveloped Reserves        
Proved developed and undeveloped reserves, beginning balance (in MBbls for Oil and NGLs/MMcf for Natural Gas) 262,045us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
[1] 214,450us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
[1] 205,023us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
 
Revisions of previous estimates (in MBbls for Oil and NGLs/MMcf for Natural Gas) (13,969)us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
(37,394)us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
(6,159)us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
 
Acquisitions of new reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 43us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
31,470us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
1,309us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
 
Extensions and discoveries (in MBbls for Oil and NGLs/MMcf for Natural Gas) 40,570us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
89,656us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
52,406us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
 
Sales of reserves in place (in MBbls for Oil and NGLs/MMcf for Natural Gas) (131,769)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
(20,269)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
(28,137)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
 
Production (in MBbls for Oil and NGLs/MMcf for Natural Gas) (14,279)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
(15,868)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
(9,992)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
 
Proved developed and undeveloped reserves, ending balance (in MBbls for Oil and NGLs/MMcf for Natural Gas) 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
[1]  
Proved developed reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 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
73,111us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
Proved undeveloped reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 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
131,912us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
Natural Gas Liquids        
Proved Developed and Undeveloped Reserves        
Proved developed and undeveloped reserves, beginning balance (in MBbls for Oil and NGLs/MMcf for Natural Gas) 67,994us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
[1] 30,335us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
[1] 47,091us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
 
Revisions of previous estimates (in MBbls for Oil and NGLs/MMcf for Natural Gas) 3,717us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
15,098us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
(3,119)us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
 
Acquisitions of new reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 13us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
683us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
224us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
 
Extensions and discoveries (in MBbls for Oil and NGLs/MMcf for Natural Gas) 18,686us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
27,259us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
3,171us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
 
Sales of reserves in place (in MBbls for Oil and NGLs/MMcf for Natural Gas) (29,067)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
(3,287)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
(15,194)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
 
Production (in MBbls for Oil and NGLs/MMcf for Natural Gas) (2,291)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
(2,094)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
(1,838)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
 
Proved developed and undeveloped reserves, ending balance (in MBbls for Oil and NGLs/MMcf for Natural Gas) 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
[1]  
Proved developed reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 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
18,854us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
Proved undeveloped reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 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
28,237us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
Natural Gas Reserves        
Proved Developed and Undeveloped Reserves        
Proved developed and undeveloped reserves, beginning balance (in MBbls for Oil and NGLs/MMcf for Natural Gas) 1,415,042us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[1] 1,355,056us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[1] 1,762,665us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
 
Revisions of previous estimates (in MBbls for Oil and NGLs/MMcf for Natural Gas) (53,432)us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
(538,214)us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
(164,845)us-gaap_ProvedDevelopedAndUndevelopedReservesRevisionsOfPreviousEstimatesIncreaseDecrease
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
 
Acquisitions of new reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 363us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
202,995us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
2,906us-gaap_ProvedDevelopedAndUndevelopedReservesPurchasesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
 
Extensions and discoveries (in MBbls for Oil and NGLs/MMcf for Natural Gas) 359,918us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
489,302us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
299,848us-gaap_ProvedDevelopedAndUndevelopedReservesExtensionsDiscoveriesAndAdditions
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[2]  
Sales of reserves in place (in MBbls for Oil and NGLs/MMcf for Natural Gas) (228,229)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
(548)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
(476,212)us-gaap_ProvedDevelopedAndUndevelopedReservesSalesOfMineralsInPlace
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
 
Production (in MBbls for Oil and NGLs/MMcf for Natural Gas) (103,233)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
(93,549)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
(69,306)us-gaap_ProvedDevelopedAndUndevelopedReservesProduction
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
 
Proved developed and undeveloped reserves, ending balance (in MBbls for Oil and NGLs/MMcf for Natural Gas) 1,390,429us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[1] 1,415,042us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[1] 1,355,056us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[1]  
Proved developed reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 951,609us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
896,701us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
670,382us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
784,292us-gaap_ProvedDevelopedReservesVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
Proved undeveloped reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 438,820us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
518,341us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
684,674us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
978,373us-gaap_ProvedUndevelopedReserveVolume
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
[1] Includes proved reserves attributable to noncontrolling interests at December 31, 2013, 2012 and 2011 as shown in the table below: December 31, 2013 2012 2011Oil (MBbl)13,569 17,340 17,018NGL (MBbl)4,737 5,132 1,782Natural gas (MMcf)69,693 94,543 45,500
[2] Natural gas reserves are computed at 14.65 pounds per square inch absolute and 60 degrees Fahrenheit.