Note 5 - Income Taxes - Changes in the Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Balance at beginning of year	$ (94,981)	$ (78,684)	$ (99,602)
Balance at end of year	(86,634)	(94,981)	(78,684)
Increase Due to Uncertainty of Recovery [Member]
Valuation allowance, deferred tax asset, increase (decrease)	2,442	(5,700)	(14,964)
Decrease Related to Utilization and Expiration [Member]
Valuation allowance, deferred tax asset, increase (decrease)	0	873	35,882
Klondex Mines Ltd [Member] | Business Acquisition [Member]
Valuation allowance, deferred tax asset, increase (decrease)	$ 5,905	$ (11,470)	$ 0