Note 5 - Income Taxes - Components of the Net Deferred Tax Asset (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accrued reclamation costs	$ 28,306	$ 29,064
Deferred exploration	13,762	16,500
Foreign net operating losses	12,013	13,231
Domestic net operating losses	175,024	152,320
Pension and benefit obligation	13,866	12,345
Foreign exchange loss	21,719	24,849
Foreign tax credit carryforward	4,149	4,149
Miscellaneous	32,926	26,290
Total deferred tax assets	301,765	278,748
Valuation allowance	(86,634)	(94,981)	$ (78,684)	$ (99,602)
Total deferred tax assets	215,131	183,767
Miscellaneous	(904)	(5,234)
Properties, plants and equipment	(348,972)	(350,083)
Total deferred tax liabilities	(349,876)	(355,317)
Net deferred tax liability	$ (134,745)	$ (171,550)