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Note 4 - Commitments, Contingencies and Obligations (Details Textual) $ in Millions |  | 1 Months Ended | 3 Months Ended | 12 Months Ended | 28 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Apr. 12, 2013 USD ($) | Aug. 31, 2012 USD ($) | Jun. 30, 2011 USD ($) | Mar. 31, 2018 USD ($) | Mar. 31, 2017 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2014 USD ($) | Mar. 05, 2018 USD ($) | Mar. 05, 2018 CAD ($)
Environmental Remediation Expense |  |  |  | $ 1,262,000 | $ 1,119,000 |  |  |  |  |
Contractual Obligation, Total |  |  |  | 7,100,000 |  |  |  |  |  |
Capital Leases, Future Minimum Payments Due, Total |  |  |  | 13,590,000 |  |  |  |  |  |
Surety Bonds |  |  |  | 117,000,000 |  |  |  |  |  |
Lucky Friday [Member] |  |  |  |  |  |  |  |  |  |
Open Purchase Orders |  |  |  | 100,000 |  |  |  |  |  |
Casa Berardi [Member] |  |  |  |  |  |  |  |  |  |
Open Purchase Orders |  |  |  | 3,100,000 |  |  |  |  |  |
Greens Creek [Member] |  |  |  |  |  |  |  |  |  |
Open Purchase Orders |  |  |  | 3,300,000 |  |  |  |  |  |
Senior Notes [Member] |  |  |  |  |  |  |  |  |  |
Proceeds from Issuance of Debt | $ 500,000,000 |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage | 6.875% |  |  |  |  |  |  |  |  |
Debt Instrument, Increase (Decrease), Net, Total |  |  |  |  |  |  | $ 6,500,000 |  |  |
Debt Instrument, Face Amount | $ 500,000,000 |  |  |  |  |  |  |  |  |
Series 2018-A Senior Notes [Member] |  |  |  |  |  |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  |  |  |  |  |  |  | 4.68% | 4.68%
Debt Instrument, Face Amount |  |  |  |  |  |  |  |  | $ 30,800,000 | $ 40
Debt Instrument, Issuance, Discount Rate |  |  |  |  |  |  |  |  | 0.58% | 0.58%
Johnny M Mine Area near San Mateo, New Mexico [Member] |  |  |  |  |  |  |  |  |  |
Payment Of Response Costs |  | $ 1,100,000 |  |  |  |  |  | $ 1,100,000 |  |
Estimated Response Costs |  |  |  | 5,600,000 |  |  |  |  |  |
Environmental Remediation Expense |  |  |  |  |  | $ 5,600,000 |  |  |  |
Johnny M Mine Area near San Mateo, New Mexico [Member] | Minimum [Member] |  |  |  |  |  |  |  |  |  |
Estimated Alternative Response Costs |  |  |  | 0 |  |  |  |  |  |
Johnny M Mine Area near San Mateo, New Mexico [Member] | Maximum [Member] |  |  |  |  |  |  |  |  |  |
Estimated Alternative Response Costs |  |  |  | $ 221,000,000 |  |  |  |  |  |
Carpenter Snow Creek Superfund Site, Cascade County, Montana [Member] |  |  |  |  |  |  |  |  |  |
Estimated Response Costs |  |  | $ 4,500,000 |  |  |  |  |  |  |
Estimated Future Response Cost |  |  | $ 100,000,000 |  |  |  |  |  |  |
Joint Venture [Member] | Rio Grande Silver Inc and Emerald Mining and Leasing LLC [Member] |  |  |  |  |  |  |  |  |  |
Equity Method Investment, Ownership Percentage |  |  |  | 70.00% |  |  |  |  |  |
Maximum Environmental Remediation Obligation |  |  |  | $ 2,500,000 |  |  |  |  |  |

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