Plant and Equipment, Net - Components of plant, equipment, and mine development, net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Plant, equipment and mine development, gross	$ 88,070	$ 88,248
Less, accumulated depreciation and amortization	(30,221)	(29,764)
Total	57,849	58,484
Leach pads
Property, Plant and Equipment [Line Items]
Plant, equipment and mine development, gross	17,431	17,431
Process equipment
Property, Plant and Equipment [Line Items]
Plant, equipment and mine development, gross	$ 17,755	17,735
Buildings and leasehold improvements
Property, Plant and Equipment [Line Items]
Useful life	10 years
Plant, equipment and mine development, gross	$ 9,280	9,280
Mine equipment
Property, Plant and Equipment [Line Items]
Plant, equipment and mine development, gross	6,026	6,224
Vehicles
Property, Plant and Equipment [Line Items]
Plant, equipment and mine development, gross	$ 1,454	1,454
Furniture and office equipment
Property, Plant and Equipment [Line Items]
Useful life	7 years
Plant, equipment and mine development, gross	$ 330	330
Construction in progress and other
Property, Plant and Equipment [Line Items]
Plant, equipment and mine development, gross	$ 35,794	$ 35,794
Minimum | Process equipment
Property, Plant and Equipment [Line Items]
Useful life	5 years
Minimum | Mine equipment
Property, Plant and Equipment [Line Items]
Useful life	5 years
Minimum | Vehicles
Property, Plant and Equipment [Line Items]
Useful life	3 years
Maximum | Process equipment
Property, Plant and Equipment [Line Items]
Useful life	15 years
Maximum | Mine equipment
Property, Plant and Equipment [Line Items]
Useful life	7 years
Maximum | Vehicles
Property, Plant and Equipment [Line Items]
Useful life	5 years