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Inventories (Tables)
3 Months Ended
Mar. 31, 2018
Inventory Disclosure [Abstract]  
Inventories
Inventories consist of the following: 
 
 
March 31,
 
December 31,
 
 
2018
 
2017
 
 
(In thousands)
Coal
 
$
63,884

 
$
54,692

Repair parts and supplies
 
79,947

 
74,268

 
 
$
143,831

 
$
128,960