Note 6 - Income Taxes - Components of the Net Deferred Tax Asset (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accrued reclamation costs	$ 29,064	$ 21,812
Deferred exploration	16,500	17,426
Foreign net operating losses	13,231	1,003
Domestic net operating losses	152,320	130,186
AMT credit carryforwards		584
Pension and benefit obligation	12,345	12,584
Foreign exchange loss	24,849	18,112
Foreign tax credit carryforward	4,149	4,983
Miscellaneous	26,290	25,411
Total deferred tax assets	278,748	232,101
Valuation allowance	(94,981)	(78,684)	$ (99,602)	$ (115,806)
Total deferred tax assets	183,767	153,417
Miscellaneous	(5,234)	(4,978)
Properties, plants and equipment	(350,083)	(271,282)
Total deferred tax liabilities	(355,317)	(276,260)
Net deferred tax liability	$ (171,550)	$ (122,843)