Note 5 - Income Taxes - Components of the Net Deferred Tax Asset (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Accrued reclamation costs	$ 21,812	$ 30,188
Deferred exploration	17,426	26,785
Foreign net operating losses	1,003	1,058
Domestic net operating losses	130,186	82,359
AMT credit carryforwards	584	20,405
Pension and benefit obligation	12,584	18,115
Foreign exchange loss	18,112	34,977
Foreign tax credit carryforward	4,983	7,283
Miscellaneous	25,411	30,166
Total deferred tax assets	232,101	251,336
Valuation allowance	(78,684)	(99,602)	$ (115,806)	$ (32,094)
Total deferred tax assets	153,417	151,734
Deferred tax liabilities:
Miscellaneous	(4,978)	(3,046)
Properties, plants and equipment	(268,476)	(235,700)
Total deferred tax liabilities	(273,454)	(238,746)
Net deferred tax liability	$ (120,037)	$ (87,012)