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Supplemental Information (Details 4)
 12 Months Ended
Dec. 31, 2012
MMBbls
Dec. 31, 2011
MMBbls
Oil [Member]
    
Proved Developed Reserves:    
Beginning of year 6,418 5,233
Extensions, discoveries and improved recovery 224 836
Revisions of previous estimates 252 273
Converted from undeveloped reserves 861 704
Reserves sold      
Reserves purchased 168  
Production (745) (628)
End of year 7,178 6,418
Proved Undeveloped Reserves:    
Beginning of year 2,435 2,652
Extensions, discoveries and improved recovery 3,446 460
Revisions of previous estimates 887 27
Converted to developed reserves (861) (704)
Reserves sold      
Reserves purchased      
End of year 5,907 2,435
Total Proved Reserves at the End of the Year 13,085 8,853
NGL's [Member]
    
Proved Developed Reserves:    
Extensions, discoveries and improved recovery 49  
Revisions of previous estimates 2,860  
End of year 2,909  
Proved Undeveloped Reserves:    
Extensions, discoveries and improved recovery 1,401  
Revisions of previous estimates 1,476  
Reserves sold     
Reserves purchased     
End of year 2,877  
Total Proved Reserves at the End of the Year 5,786  
Gas [Member]
    
Proved Developed Reserves:    
Beginning of year 43,631 41,946
Extensions, discoveries and improved recovery 1,000 3,536
Revisions of previous estimates (15,821) 121
Converted from undeveloped reserves 3,527 3,028
Reserves sold      
Reserves purchased 211  
Production (4,715) (5,000)
End of year 27,833 43,631
Proved Undeveloped Reserves:    
Beginning of year 9,765 11,400
Extensions, discoveries and improved recovery 6,158 1,955
Revisions of previous estimates 217 (562)
Converted to developed reserves (3,527) (3,028)
Reserves sold     
Reserves purchased     
End of year 12,613 9,765
Total Proved Reserves at the End of the Year 40,446 53,396