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Note 15 - Derivatives (Tables)
6 Months Ended
Jun. 30, 2021
Notes Tables  
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]
  

June 30, 2021

  

December 31, 2020

 
  

Asset Derivatives

  

Liability Derivatives

  

Asset Derivatives

  

Liability Derivatives

 

Coal Contracts Related to Forecasted Sales

 $160  $(20,597) $  $ 

Effect of Counterparty Netting

  (160)  160       

Net Derivatives as Classified in the Consolidated Balance Sheets

 $  $(20,437) $  $