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Asset Retirement Obligation (Changes in Asset Retirement Obligations) (Detail) - USD ($)
9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Reconciliation Of Changes In Asset Retirement Obligations [Line Items]    
Asset retirement obligations, December 31, 2014 $ 2,906,093  
Liabilities incurred during the period 0  
Liabilities settled during the period (2,244)  
Accretion 206,397 $ 191,348
Asset retirement obligations, September 30, 2015 $ 3,110,245