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Inventories
9 Months Ended
Sep. 30, 2017
Inventory Disclosure [Abstract]  
Inventories
Inventories

Inventories are summarized as follows:

 
SEPTEMBER 30
2017
 
DECEMBER 31
2016
Coal
$
14,695

 
$
13,137

Mining supplies
15,885

 
15,790

 Total inventories
$
30,580

 
$
28,927