Note 4 - Environmental and Reclamation Activities - Accrued Reclamation and Closure Cost Liability Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Balance	$ 108,389	$ 86,045	$ 85,580
Accruals for estimated costs	472	250	16
Accretion expense	7,122	5,309	4,870
Revision of estimated cash flows due to changes in reclamation plans	(4,522)	1,280	(578)
Payment of reclamation obligations	(3,087)	(4,066)	(3,843)
Liability addition due to acquisition		19,571
Balance	$ 108,374	$ 108,389	$ 86,045