Note 5 - Environmental and Reclamation Activities - Accrued Reclamation and Closure Cost Liability Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Balance	$ 86,045	$ 85,580	$ 95,538
Accruals for estimated costs	250	16	705
Accretion expense	5,309	4,870	3,158
Revision of estimated cash flows due to changes in reclamation plans	1,280	(578)	2,759
Liability addition due to acquisition	19,571		1,124
Payment of reclamation obligations	(4,066)	(3,843)	(17,704)
Balance	$ 108,389	$ 86,045	$ 85,580