Property, Plant and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Property, plant and equipment
Property, plant and equipment, gross	$ 35,387	$ 35,418
Less: Accumulated depreciation and amortization	(29,104)	(29,002)
Property, plant and equipment, net	6,283	6,416
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	3,808	3,808
Mining equipment and machinery
Property, plant and equipment
Property, plant and equipment, gross	17,074	17,127
Other furniture and equipment
Property, plant and equipment
Property, plant and equipment, gross	1,377	1,355
Asset retirement cost
Property, plant and equipment
Property, plant and equipment, gross	$ 1,157	$ 1,157