Property, Plant and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Property, plant and equipment
Property, plant and equipment, gross	$ 35,311	$ 35,639
Less: Accumulated depreciation and amortization	(28,907)	(29,012)
Property, plant and equipment, net	6,404	6,627
Mineral properties
Property, plant and equipment
Property, plant and equipment, gross	9,353	9,353
Exploration properties
Property, plant and equipment
Property, plant and equipment, gross	2,418	2,418
Royalty properties
Property, plant and equipment
Property, plant and equipment, gross	200	200
Buildings
Property, plant and equipment
Property, plant and equipment, gross	3,806	3,806
Mining equipment and machinery
Property, plant and equipment
Property, plant and equipment, gross	17,144	17,477
Other furniture and equipment
Property, plant and equipment
Property, plant and equipment, gross	1,333	1,328
Asset retirement cost
Property, plant and equipment
Property, plant and equipment, gross	$ 1,057	$ 1,057