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Note 5 - Environmental and Reclamation Activities (Details Textual)
$ in Thousands
1 Months Ended 3 Months Ended 9 Months Ended 12 Months Ended
Nov. 07, 2016
USD ($)
Aug. 31, 2016
USD ($)
Dec. 31, 2018
USD ($)
Jun. 30, 2015
USD ($)
Sep. 30, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Accrual for Environmental Loss Contingencies, Ending Balance     $ 108,389     $ 86,045 $ 85,580 $ 95,538
Greens Creek [Member]                
Asset Retirement Obligation, Revision of Estimate Before Discounting     114,900   $ 100,100      
Asset Retirement Obligation, Liabilities Incurred     3,200          
San Sebastian [Member]                
Asset Retirement Obligation, Revision of Estimate Before Discounting     2,800          
Asset Retirement Obligation, Liabilities Incurred     2,300          
Nevada Operations [Member]                
Asset Retirement Obligation, Revision of Estimate Before Discounting     1,300          
Asset Retirement Obligation, Liabilities Incurred     $ 3,100          
Asset Retirement Obligation [Member] | Measurement Input, Risk Free Interest Rate [Member]                
Derivative Liability, Measurement Input     0.075          
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    
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    
Nelson Tunnel/Commodore Site [Member] | United States and Colorado [Member]                
Loss Contingency Accrual, Payments   $ 6,000            
Gilt Edge Mine Superfund Site [Member] | United States and South Dakota [Member]                
Loss Contingency Accrual, Payments $ 3,900              
Gilt Edge Mine Superfund Site [Member] | United States, South Dakota, Insurers and Another Potentially Responsible Party [Member]                
Loss Contingency Accrual, Payments $ 6,700              
Gilt Edge Site and Nelson Tunnel/Commodore Site [Member]                
Liability for Remediation       $ 9,900