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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) 126,031us-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] 214,450us-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) 91,786us-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] 30,335us-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) 1,788,233us-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] 1,355,056us-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) 11,027us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember		 13,569us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember		 17,340us-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) 4,761us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember		 4,737us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember		 5,132us-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) 70,833us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember		 69,693us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember		 94,543us-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.