v2.4.0.6
Working Interest Acquisitions - Additional Information (Detail) (USD $)
 3 Months Ended 12 Months Ended 1 Months Ended
Dec. 31, 2012
Sep. 30, 2012
Jun. 30, 2012
Mar. 31, 2012
Dec. 31, 2011
Sep. 30, 2011
Jun. 30, 2011
Mar. 31, 2011
Dec. 31, 2010
Sep. 30, 2010
Jun. 30, 2010
Mar. 31, 2010
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Feb. 28, 2011
Project Pangea [Member]
Oct. 31, 2010
Project Pangea [Member]
Business Acquisition [Line Items]                                  
Percentage of additional working interest acquired                               38.00% 10.00%
Additional working interest from non-operating partners                               $ 70,800,000 $ 21,200,000
Oil, NGL and gas sales 35,309,000 33,038,000 29,927,000 30,618,000 31,123,000 27,958,000 29,123,000 20,183,000 16,290,000 14,916,000 13,155,000 13,220,000 128,892,000 108,387,000 57,581,000 25,500,000 1,300,000
Net income $ (837,000) $ (2,355,000) $ 7,862,000 $ 1,714,000 $ (9,285,000) $ 7,073,000 $ 7,990,000 $ 1,464,000 $ 261,000 $ 2,087,000 $ 1,551,000 $ 3,563,000 $ 6,384,000 $ 7,242,000 $ 7,462,000 $ 8,400,000 $ 477,000