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Inventories (Tables)
6 Months Ended
Jun. 30, 2018
Inventory Disclosure [Abstract]  
Inventories
Inventories consist of the following: 
 
 
June 30,
 
December 31,
 
 
2018
 
2017
 
 
(In thousands)
Coal
 
$
72,268

 
$
54,692

Repair parts and supplies
 
84,937

 
74,268

 
 
$
157,205

 
$
128,960