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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) 262,045 [1] 214,450 [1] 205,023  
Revisions of previous estimates (in MBbls for Oil and NGLs/MMcf for Natural Gas) (13,969) (37,394) (6,159)  
Acquisitions of new reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 43 31,470 1,309  
Extensions and discoveries (in MBbls for Oil and NGLs/MMcf for Natural Gas) 40,570 89,656 52,406  
Sales of reserves in place (in MBbls for Oil and NGLs/MMcf for Natural Gas) (131,769) (20,269) (28,137)  
Production (in MBbls for Oil and NGLs/MMcf for Natural Gas) (14,279) (15,868) (9,992)  
Proved developed and undeveloped reserves, ending balance (in MBbls for Oil and NGLs/MMcf for Natural Gas) 142,641 [1] 262,045 [1] 214,450 [1]  
Proved developed reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 83,893 136,605 101,578 73,111
Proved undeveloped reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 58,748 125,440 112,872 131,912
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) 67,994 [1] 30,335 [1] 47,091  
Revisions of previous estimates (in MBbls for Oil and NGLs/MMcf for Natural Gas) 3,717 15,098 (3,119)  
Acquisitions of new reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 13 683 224  
Extensions and discoveries (in MBbls for Oil and NGLs/MMcf for Natural Gas) 18,686 27,259 3,171  
Sales of reserves in place (in MBbls for Oil and NGLs/MMcf for Natural Gas) (29,067) (3,287) (15,194)  
Production (in MBbls for Oil and NGLs/MMcf for Natural Gas) (2,291) (2,094) (1,838)  
Proved developed and undeveloped reserves, ending balance (in MBbls for Oil and NGLs/MMcf for Natural Gas) 59,052 [1] 67,994 [1] 30,335 [1]  
Proved developed reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 35,807 33,785 17,150 18,854
Proved undeveloped reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 23,245 34,209 13,185 28,237
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) 1,415,042 [1],[2] 1,355,056 [1],[2] 1,762,665 [2]  
Revisions of previous estimates (in MBbls for Oil and NGLs/MMcf for Natural Gas) (53,432) [2] (538,214) [2] (164,845) [2]  
Acquisitions of new reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 363 [2] 202,995 [2] 2,906 [2]  
Extensions and discoveries (in MBbls for Oil and NGLs/MMcf for Natural Gas) 359,918 [2] 489,302 [2] 299,848 [2]  
Sales of reserves in place (in MBbls for Oil and NGLs/MMcf for Natural Gas) (228,229) [2] (548) [2] (476,212) [2]  
Production (in MBbls for Oil and NGLs/MMcf for Natural Gas) (103,233) [2] (93,549) [2] (69,306) [2]  
Proved developed and undeveloped reserves, ending balance (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]  
Proved developed reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 951,609 [2] 896,701 [2] 670,382 [2] 784,292 [2]
Proved undeveloped reserves (in MBbls for Oil and NGLs/MMcf for Natural Gas) 438,820 [2] 518,341 [2] 684,674 [2] 978,373 [2]
[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.