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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 |  |  |  |

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