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Inventories (Tables)
3 Months Ended
Mar. 31, 2017
Inventory Disclosure [Abstract]  
Inventory components
 
March 31,
2017
 
December 31,
2016
Coal
$
12,626

 
$
7,800

Supplies
56,992

 
57,661

Total Inventories
$
69,618

 
$
65,461