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PROPERTY, PLANT AND EQUIPMENT - Net Book Value of Property, Plant and Equipment (Details) - USD ($)
$ in Thousands
 6 Months Ended
Jun. 30, 2021
Dec. 31, 2020
Property, Plant and Equipment [Line Items]    
Total Property, Plant and Equipment $ 8,983 $ 8,985
Impairment 0  
Mineral rights and properties    
Property, Plant and Equipment [Line Items]    
Total Property, Plant and Equipment 8,972 8,972
Other property, plant and equipment    
Property, Plant and Equipment [Line Items]    
Total Property, Plant and Equipment 11 13
Alabama    
Property, Plant and Equipment [Line Items]    
Total Property, Plant and Equipment 8,972 8,972
Alabama | Mineral rights and properties    
Property, Plant and Equipment [Line Items]    
Total Property, Plant and Equipment 8,972 8,972
Corporate    
Property, Plant and Equipment [Line Items]    
Total Property, Plant and Equipment 11 13
Corporate | Other property, plant and equipment    
Property, Plant and Equipment [Line Items]    
Total Property, Plant and Equipment $ 11 $ 13