Note 4 - Income and Mining Taxes - Major Components of Income Tax Provision (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended						6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Domestic	$ (2,176)			$ (705)					$ (7,489)	$ 1,690
Foreign	(1,578)			(2,286)					(4,690)	(6,005)
Total current income and mining tax provision	(3,754)			(2,991)					(12,179)	(7,695)
Domestic	3,213			(2,761)					8,226	(1,108)
Foreign	5,074			571					7,877	1,380
Total deferred income and mining tax benefit	8,287			(2,190)					16,103	272
Total income and mining tax benefit (provision)	$ 4,533	$ 4,134	$ (4,743)	$ (5,181)	$ (2,646)	$ 405	$ (609)	$ (2,242)	$ 3,924	$ (7,423)	$ (8,199)	$ 18,318	$ 2,445