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INVENTORIES (Details) - USD ($)
$ in Thousands
6 Months Ended
Jun. 30, 2020
Dec. 31, 2019
INVENTORIES    
Coal $ 51,418 $ 63,645
Supplies (net of reserve for obsolescence of $5,762 and $5,555, respectively) 36,975 37,660
Total inventories, net 88,393 101,305
Reserve for obsolescence 5,762 $ 5,555
Reduce inventory carrying value to market $ 16,900