PROPERTY, PLANT AND EQUIPMENT - Net Book Value of Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	$ 10,480	$ 8,985
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	1,408	13
Construction in progress
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	100
Alabama
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	10,450	8,972
Alabama | Mineral rights and properties
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	8,972	8,972
Alabama | Other property, plant and equipment
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	1,378
Alabama | Construction in progress
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	100
Corporate
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	30	13
Corporate | Other property, plant and equipment
Property, Plant and Equipment [Line Items]
Total Property, Plant and Equipment	$ 30	$ 13