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Note 20 - Concentration of Credit Risk and Major Customers (Tables)
12 Months Ended
Dec. 31, 2020
Notes Tables  
Schedules of Concentration of Risk, by Risk Factor [Table Text Block]
  

December 31,

 
  

2020

  

2019

 

Thermal coal utilities

 $32,343  $58,557 

Coal exporters and distributors

  82,948   73,416 

Steel and coke producers

  5,302    

Other

  2,122   1,815 

Total Trade Receivables

  122,715   133,788 

Less: Allowance for credit losses

  4,426   2,100 

Total Trade Receivables, net

 $118,289  $131,688