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Inventories (Tables)
6 Months Ended
Jun. 30, 2022
Inventory Disclosure [Abstract]  
Schedule of Inventories
Inventories are summarized as follows:
 JUNE 30
2022
 DECEMBER 31
2021
Coal$16,855 $19,352 
Mining supplies40,101 34,733 
 Total inventories$56,956  $54,085