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Supplementary Information - Reserve Quantity Information (Detail)
 12 Months Ended
Dec. 31, 2013
MBbls
Dec. 31, 2012
MBbls
Oil [Member]
    
Proved Developed Reserves:    
Beginning of year 7,178 6,418
Extensions, discoveries and improved recovery 87 224
Revisions of previous estimates (361) 252
Converted from undeveloped reserves 513 861
Reserves sold      
Reserves purchased   168
Production (730) (745)
End of year 6,687 7,178
Proved Undeveloped Reserves:    
Beginning of year 5,907 2,435
Extensions, discoveries and improved recovery 4,536 3,446
Revisions of previous estimates 864 887
Converted to developed reserves (513) (861)
Reserves sold      
Reserves purchased      
End of year 9,066 5,907
Total Proved Reserves at the End of the Year 15,753 13,085
NGLs [Member]
    
Proved Developed Reserves:    
Beginning of year 2,909  
Extensions, discoveries and improved recovery   49
Revisions of previous estimates (712) 2,860
Converted from undeveloped reserves 199  
Reserves sold      
Production (173)  
End of year 2,223 2,909
Proved Undeveloped Reserves:    
Beginning of year 2,877  
Extensions, discoveries and improved recovery 1,541 1,401
Revisions of previous estimates (512) 1,476
Converted to developed reserves (199)  
Reserves sold      
Reserves purchased      
End of year 3,707 2,877
Total Proved Reserves at the End of the Year 5,930 5,786
Gas [Member]
    
Proved Developed Reserves:    
Beginning of year 27,833 43,631
Extensions, discoveries and improved recovery 402 1,000
Revisions of previous estimates 6,456 (15,821)
Converted from undeveloped reserves 1,207 3,527
Reserves sold      
Reserves purchased   211
Production (4,270) (4,715)
End of year 31,628 27,833
Proved Undeveloped Reserves:    
Beginning of year 12,613 9,765
Extensions, discoveries and improved recovery 9,538 6,158
Revisions of previous estimates (1,172) 217
Converted to developed reserves (1,207) (3,527)
Reserves sold      
Reserves purchased      
End of year 19,772 12,613
Total Proved Reserves at the End of the Year 51,400 40,446