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Note 20 - Concentration of Credit Risk and Major Customers (Tables)
12 Months Ended
Dec. 31, 2021
Notes Tables  
Schedules of Concentration of Risk, by Risk Factor [Table Text Block]
  

December 31,

 
  

2021

  

2020

 

Thermal coal utilities

 $41,582  $32,343 

Coal exporters and distributors

  53,949   82,948 

Steel and coke producers

  11,560   5,302 

Other

  1,605   2,122 

Total Trade Receivables

  108,696   122,715 

Less: Allowance for credit losses

  4,597   4,426 

Total Trade Receivables, net

 $104,099  $118,289