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Inventories
9 Months Ended
Sep. 30, 2020
Inventory Disclosure [Abstract]  
Inventories Inventories
Inventories are summarized as follows:
 SEPTEMBER 30
2020
 DECEMBER 31
2019
Coal$12,161 $15,700 
Mining supplies30,272 24,765 
 Total inventories$42,433  $40,465