PROPERTY, PLANT, EQUIPMENT, AND MINERAL PROPERTIES (Schedule of Property, Plant, Equipment, and Mineral Properties) (Details) - USD ($) $ in Thousands	Sep. 30, 2026	Dec. 31, 2025
Property, Plant, and Equipment [Line Items]
Total property, plant, equipment, and mineral properties, gross	$ 724,996	$ 701,039
Less: accumulated depreciation, depletion, and amortization	(427,518)	(402,283)
Total property, plant, equipment and mineral properties, net	297,478	298,756
Land [Member]
Property, Plant, and Equipment [Line Items]
Total property, plant, equipment, and mineral properties, gross	519	519
Ponds and Land Improvements [Member]
Property, Plant, and Equipment [Line Items]
Total property, plant, equipment, and mineral properties, gross	87,863	87,881
Mineral Properties And Development Costs [Member]
Property, Plant, and Equipment [Line Items]
Total property, plant, equipment, and mineral properties, gross	157,704	155,221
Buildings and Plant [Member]
Property, Plant, and Equipment [Line Items]
Total property, plant, equipment, and mineral properties, gross	99,725	97,924
Machinery and Equipment [Member]
Property, Plant, and Equipment [Line Items]
Total property, plant, equipment, and mineral properties, gross	336,142	324,327
Vehicles [Member]
Property, Plant, and Equipment [Line Items]
Total property, plant, equipment, and mineral properties, gross	8,387	8,061
Office Equipment and Improvements [Member]
Property, Plant, and Equipment [Line Items]
Total property, plant, equipment, and mineral properties, gross	9,569	10,000
Operating Lease ROU Assets [Member]
Property, Plant, and Equipment [Line Items]
Total property, plant, equipment, and mineral properties, gross	3,027	3,181
Construction in Progress [Member]
Property, Plant, and Equipment [Line Items]
Total property, plant, equipment, and mineral properties, gross	$ 22,060	$ 13,925