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Note 5 - Asset Retirement Obligations
 9 Months Ended
Sep. 30, 2017
Notes to Financial Statements  
Asset Retirement Obligation Disclosure [Text Block]
5.
         Asset Retirement Obligations
 
 
Changes in the carrying amount of our asset retirement obligations were as follows:
 
 
   
Three Months Ended
September
30,
    
Nine Months
Ended
September
30,
  
   
2017
   
2016
   
2017
    
2016
  
                                 
Balance at beginning of period
   $
10,810,108
     $
2,135,342
     $
10,128,634
     $
2,095,073
  
Additional retirement obligations incurred
    
950,953
      
7,416,164
      
1,429,874
      
7,416,164
  
Accretion expense
    
101,276
      
94,519
      
303,829
      
134,788
  
Balance at end of period
   $
11,862,337
     $
9,646,025
     $
11,862,337
     $
9,646,025