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Working Interest Acquisitions - Condensed Unaudited Pro Forma Information (Detail) (USD $)
In Thousands, except Per Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Schedule Of Business Acquisition By Acquisition Financial Results [Line Items]    
Oil, NGL and gas sales $ 113,041 $ 86,114
Total operating expenses 100,125 63,384
Net income (loss) $ 7,186 $ 15,714
Earnings (loss) per share - basic $ 0.25 $ 0.71
Earnings (loss) per share - diluted $ 0.25 $ 0.71