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Note 4 - Environmental and Reclamation Activities (Details Textual)
$ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Accrual for Environmental Loss Contingencies, Ending Balance $ 108,374 $ 108,389 $ 108,374 $ 86,045 $ 85,580
Lucky Friday [Member]          
Asset Retirement Obligation, Revision of Estimate Before Discounting 34,300 $ 31,800      
Asset Retirement Obligation, Liabilities Incurred 1,100        
San Sebastian [Member]          
Asset Retirement Obligation, Revision of Estimate Before Discounting 500        
Asset Retirement Obligation, Liabilities Incurred 1,200        
Nevada Operations [Member]          
Asset Retirement Obligation, Revision of Estimate Before Discounting 200        
Asset Retirement Obligation, Liabilities Incurred 500        
Casa Berardi [Member]          
Asset Retirement Obligation, Revision of Estimate Before Discounting 2,200        
Asset Retirement Obligation, Liabilities Incurred $ 2,200        
Minimum [Member]          
Inflation Rate, Asset Retirement Obligation     2.00%    
Minimum [Member] | Reclamation and Abandonment Costs [Member] | Measurement Input, Risk Free Interest Rate [Member]          
Derivative Liability, Measurement Input 0.0575   0.0575    
Minimum [Member] | Asset Retirement Obligation [Member] | Measurement Input, Risk Free Interest Rate [Member]          
Derivative Liability, Measurement Input 0.070   0.070    
Maximum [Member]          
Inflation Rate, Asset Retirement Obligation     4.00%    
Maximum [Member] | Reclamation and Abandonment Costs [Member] | Measurement Input, Risk Free Interest Rate [Member]          
Derivative Liability, Measurement Input 0.145   0.145    
Maximum [Member] | Asset Retirement Obligation [Member] | Measurement Input, Risk Free Interest Rate [Member]          
Derivative Liability, Measurement Input 0.075   0.075