Note 3 - Property, Plant and Equipment - Depreciation and amortization (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment
Depreciation of plant and equipment	$ 17,945	$ 17,094	$ 14,219
Depreciation of right of use assets	1,109
Amortization of capitalized mine development costs	7,151	3,818	5,302
Total depreciation and amortization	$ 26,205	$ 20,912	$ 19,521