v2.4.0.6
Disclosures About Oil and Gas Producing Activities - Summary of Changes in Quantities of Proved Oil, NGL and Natural Gas Reserves (Detail)
12 Months Ended
Dec. 31, 2012
MBoe
Dec. 31, 2011
MBoe
Dec. 31, 2010
MBoe
Reserve Quantities [Line Items]      
Proved Developed and Proved Undeveloped Reserves,Mboe Beginning Balance 76,975 50,715 36,488
Extensions and discoveries, Mboe 38,861 25,548 3,773
Purchases of minerals in place, Mboe   10,498 1,958
Production, Mboe (2,888) (2,338) (1,556)
Revisions to previous estimates, Mboe (17,469) (7,448) 10,052
Proved Developed and Proved Undeveloped Reserves, Mboe Ending Balance 95,479 76,975 50,715
Beginning Balance, Proved Developed Reserves, Mboe 33,611 25,795 15,585
Ending Balance, Proved Developed Reserves, Mboe 32,774 33,611 25,795
Beginning Balance, Proved Undeveloped Reserves, Mboe 43,365 24,920 20,903
Ending Balance, Proved undeveloped Reserves, Mboe 62,705 43,365 24,920
Natural Gas (MMcf) [Member]
     
Reserve Quantities [Line Items]      
Proved Developed and Proved Undeveloped Reserves, Beginning Balance 178,807 150,389 168,334
Extensions and discoveries 49,372 40,146 8,365
Purchases of minerals in place   24,083 4,736
Production (6,089) (6,345) (6,290)
Revisions to previous estimates (47,330) (29,466) (24,756)
Proved Developed and Proved Undeveloped Reserves, Ending Balance 174,760 178,807 150,389
Beginning Balance, Proved Developed Reserve, MMcf 84,743 74,739 74,804
Ending Balance, Proved Developed Reserve, MMcf 73,178 84,743 74,739
Beginning Balance, Proved Undeveloped Reserves, MMcf 94,064 75,650 93,530
Ending Balance, Proved Undeveloped Reserves, MMcf 101,582 94,064 75,650
NGLs (MBbls) [Member]
     
Reserve Quantities [Line Items]      
Proved Developed and Proved Undeveloped Reserves, Beginning Balance 29,123 20,699 4,094
Extensions and discoveries 8,639 7,010 1,395
Purchases of minerals in place   4,284 786
Production (904) (798) (261)
Revisions to previous estimates (7,758) (2,072) 14,685
Proved Developed and Proved Undeveloped Reserves, Ending Balance 29,100 29,123 20,699
Beginning Balance, Proved Developed Reserves, MBbls 13,945 11,193 1,879
Ending Balance, Proved Developed Reserves, MBbls 11,761 13,945 11,193
Beginning Balance, Proved Undeveloped Reserves, MBbls 15,178 9,506 2,215
Ending Balance, Proved Undeveloped Reserves, MBbls 17,339 15,178 9,506
Oil (MBbls) [Member]
     
Reserve Quantities [Line Items]      
Proved Developed and Proved Undeveloped Reserves, Beginning Balance 18,051 4,951 4,338
Extensions and discoveries 21,993 11,847 984
Purchases of minerals in place   2,200 383
Production (969) (482) (247)
Revisions to previous estimates (1,823) (465) (507)
Proved Developed and Proved Undeveloped Reserves, Ending Balance 37,252 18,051 4,951
Beginning Balance, Proved Developed Oil Reserves, MBbls 5,542 2,146 1,239
Ending Balance, Proved Developed Oil Reserves, MBbls 8,816 5,542 2,146
Beginning Balance, Proved Undeveloped Oil Reserves, MBbls 12,509 2,805 3,099
Ending Balance, Proved Undeveloped Oil Reserves, MBbls 28,436 12,509 2,805