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Inventories
9 Months Ended
Sep. 30, 2021
Inventory Disclosure [Abstract]  
Inventories Inventories
Inventories are summarized as follows:
 SEPTEMBER 30
2021
 DECEMBER 31
2020
Coal$17,172 $17,695 
Mining supplies33,783 29,856 
 Total inventories$50,955  $47,551