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