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Standardized Measure of Discounted Future Net Cash Flows (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]    
Future production revenue $ 246,535,000 $ 242,383,840
Future production costs (69,131,000) (93,373,850)
Future development costs (11,766,000) (12,767,540)
Future cash flows before income tax 165,638,000 136,242,450
Future income taxes (33,550,000) (22,864,737)
Future net cash flows 132,088,000 113,377,713
10% annual discount for estimating of future cash flows (83,215,000) (69,730,808)
Standardized measure of discounted net cash flows $ 48,873,000 $ 43,646,905