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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) 142,641 [1] 262,045 [1] 214,450 [1] 205,023
Natural Gas Liquids
        
Reserve Quantities [Line Items]        
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 59,052 [1] 67,994 [1] 30,335 [1] 47,091
Natural Gas Reserves
        
Reserve Quantities [Line Items]        
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 1,390,429 [1],[2] 1,415,042 [1],[2] 1,355,056 [1],[2] 1,762,665 [2]
Noncontrolling Interest | Oil Reserves
        
Reserve Quantities [Line Items]        
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 13,569 17,340 17,018  
Noncontrolling Interest | Natural Gas Liquids
        
Reserve Quantities [Line Items]        
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 4,737 5,132 1,782  
Noncontrolling Interest | Natural Gas Reserves
        
Reserve Quantities [Line Items]        
Proved reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 69,693 94,543 45,500  
[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.