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Supplemental Oil And Gas Reserve Information - Unaudited (Net Proved, Proved Developed And Proved Undeveloped Reserves) (Details)
 12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Reserve Quantities [Line Items]      
Extensions, discoveries and other additions 43,168    
Oil MBbl [Member]
      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 36,550 12,421 2,193
Revisions of previous estimates (262) 2,235 781
Extensions, discoveries and other additions 36,464 22,445 8,381
Sales of reserves in place (56) (122) (2)
Purchases of reserves in place 100 1,363 1,726
Production (3,732) (1,792) (658)
Net proved reserves, closing balance 69,064 36,550 12,421
Oil MBbl [Member] | Proved Developed Reserves [Member]
      
Reserve Quantities [Line Items]      
Net proved reserves, closing balance 31,749 15,650 5,231
Oil MBbl [Member] | Proved Undeveloped Reserves [Member]
      
Reserve Quantities [Line Items]      
Net proved reserves, closing balance 37,315 20,900 7,190
Gas MMcf [Member]
      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 19,379 5,270 671
Revisions of previous estimates (159) 1,897 (84)
Extensions, discoveries and other additions 40,220 12,172 3,414
Sales of reserves in place (518) (5) (16)
Purchases of reserves in place 65 696 1,611
Production (1,087) (651) (326)
Net proved reserves, closing balance 57,900 19,379 5,270
Gas MMcf [Member] | Proved Developed Reserves [Member]
      
Reserve Quantities [Line Items]      
Net proved reserves, closing balance 24,535 8,208 2,293
Gas MMcf [Member] | Proved Undeveloped Reserves [Member]
      
Reserve Quantities [Line Items]      
Net proved reserves, closing balance 33,365 11,171 2,977
MBoe [Member]
      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 39,780 13,299 2,304
Revisions of previous estimates (288) 2,552 767
Extensions, discoveries and other additions 43,168 24,473 8,950
Sales of reserves in place (142) (123) (5)
Purchases of reserves in place 111 1,479 1,995
Production (3,914) (1,900) (712)
Net proved reserves, closing balance 78,715 39,780 13,299
MBoe [Member] | Proved Developed Reserves [Member]
      
Reserve Quantities [Line Items]      
Net proved reserves, closing balance 35,839 17,018 5,613
MBoe [Member] | Proved Undeveloped Reserves [Member]
      
Reserve Quantities [Line Items]      
Net proved reserves, closing balance 42,876 22,762 7,686