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Asset retirement obligations (Details) (USD $)
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Dec. 31, 2012
Asset Retirement Obligations Details          
Asset retirement obligations, beginning     $ 3,317,358 $ 1,186,260 $ 1,186,260
Disposal of assets          (88,650)
Settlement of liabilities          (55,915)
Revision of previous estimates          1,797,626
Accretion expense 36,723 29,353 71,702 34,241 94,556
Additions     10,036    383,481
Asset retirement obligations, ending 3,399,096   3,399,096   3,317,358
Less: current portion 542,443   542,443   452,013
Long-term portion $ 2,856,653   $ 2,856,653   $ 2,865,345