Note 6 - Income Taxes - Changes in the Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Balance at beginning of year	$ (86,634)	$ (94,981)	$ (78,684)
Balance at end of year	(77,210)	(86,634)	(94,981)
Increase Due to Uncertainty of Recovery [Member]
Valuation allowance, deferred tax asset, increase (decrease)	786	686	(5,700)
Decrease Related to Utilization and Expiration [Member]
Valuation allowance, deferred tax asset, increase (decrease)	8,638	1,756	873
Klondex Mines Ltd [Member] | Business Acquisition [Member]
Valuation allowance, deferred tax asset, increase (decrease)	$ 0	$ 5,905	$ (11,470)