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Note 4 - Other Long-term Assets (Tables)
9 Months Ended
Sep. 30, 2022
Notes Tables  
Schedule of Other Assets, Noncurrent [Table Text Block]
  

September 30,

  

December 31,

 
  

2022

  

2021

 

Advanced coal royalties

 $6,181  $6,678 

Other

  1,647   1,694 

Total other assets

 $7,828  $8,372