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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, 2013
MBbls
Dec. 31, 2012
MBbls
Dec. 31, 2011
MBbls
Dec. 31, 2010
MBbls
Oil Reserves        
Reserve Quantities [Line Items]        
Proved reserves (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] 205,023us-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) 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] 47,091us-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) 1,390,429us-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] 1,762,665us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasReservesMember
Noncontrolling Interest | Oil Reserves        
Reserve Quantities [Line Items]        
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 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
17,018us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_OilReservesMember
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
 
Noncontrolling Interest | Natural Gas Liquids        
Reserve Quantities [Line Items]        
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 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
1,782us-gaap_ProvedDevelopedAndUndevelopedReservesNet
/ us-gaap_ReserveQuantitiesByTypeOfReserveAxis
= us-gaap_NaturalGasLiquidsReservesMember
/ us-gaap_StatementEquityComponentsAxis
= us-gaap_NoncontrollingInterestMember
 
Noncontrolling Interest | Natural Gas Reserves        
Reserve Quantities [Line Items]        
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 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
45,500us-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, 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