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Inventories (Tables)
12 Months Ended
Dec. 31, 2017
Inventory Disclosure [Abstract]  
Inventories
Inventories consist of the following: 
 
 
December 31, 2017
 
December 31, 2016
(In thousands)
 
 
 
 
Coal
 
$
54,692

 
$
37,268

Repair parts and supplies
 
74,268

 
76,194

 
 
$
128,960

 
$
113,462