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Inventories (Tables)
9 Months Ended
Sep. 30, 2019
Inventory Disclosure [Abstract]  
Schedule of Inventories
Inventories are summarized as follows:
 
SEPTEMBER 30
2019
 
DECEMBER 31
2018
Coal
$
8,416

 
$
11,030

Mining supplies
24,671

 
20,179

 Total inventories
$
33,087

 
$
31,209