Note 3 - Income and Mining Taxes (Details Textual) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	$ (3,400)		$ (8,600)
Income Tax Expense (Benefit), Total	(4,842)	$ 626	$ (208)	$ (436)
Recognition of Previously Omitted Deferred Income Taxes on Certain State Mining Income Taxes [Member]
Income Tax Expense (Benefit), Total	$ 3,500	$ 6,500