Note 5 - Environmental and Reclamation Activities - Accrued Reclamation and Closure Cost Liability Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Balance	$ 108,374	$ 108,389	$ 86,045
Accruals for estimated costs		472	250
Accretion expense	5,912	7,122	5,309
Revision of estimated cash flows due to changes in reclamation plans	2,543	(4,522)	1,280
Liability addition due to acquisition			19,571
Payment of reclamation obligations	(781)	(3,087)	(4,066)
Balance	$ 116,048	$ 108,374	$ 108,389