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Note 4 - Inventories (Tables)
12 Months Ended
Dec. 31, 2019
Notes Tables  
Schedule of Inventory, Current [Table Text Block]
   
December 31,
 
   
2019
   
2018
 
Parts inventory
  $
87,625
    $
82,384
 
Fuel inventory
   
79,497
     
76,761
 
Other inventory
   
14,082
     
11,720
 
Total inventory
  $
181,204
    $
170,865