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Inventories (Tables)
 12 Months Ended
Dec. 31, 2017
Inventory Disclosure [Abstract]  
Schedule of Inventory Components
Inventory components consist of the following:
 
December 31,
 
2017
 
2016
Coal
$
11,411

 
$
7,800

Supplies
42,009

 
42,361

Total Inventories
$
53,420

 
$
50,161