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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) (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 Developed and Undeveloped Reserves, Net 142,641 [1] 262,045 [1] 214,450 [1] 205,023
Natural Gas Liquids
        
Reserve Quantities [Line Items]        
Proved Developed and Undeveloped Reserves, Net 59,052 [1] 67,994 [1] 30,335 [1] 47,091
Natural Gas Reserves
        
Reserve Quantities [Line Items]        
Proved Developed and Undeveloped Reserves, Net 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 Developed and Undeveloped Reserves, Net 13,569 17,340 17,018  
Noncontrolling Interest | Natural Gas Liquids
        
Reserve Quantities [Line Items]        
Proved Developed and Undeveloped Reserves, Net 4,737 5,132 1,782  
Noncontrolling Interest | Natural Gas Reserves
        
Reserve Quantities [Line Items]        
Proved Developed and Undeveloped Reserves, Net 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.