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Note 1 - Summary of Significant Accounting Policies (Details Textual) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2016 USD ($) oz T | Dec. 31, 2015 USD ($) | Dec. 31, 2014 USD ($)
Capitalized Drilling Costs | $ 6,800 | $ 6,700 | $ 5,300
Foreign Currency Transaction Gain (Loss), Realized | (2,926) | 24,551 | $ 11,535
Deferred Tax Assets, Net of Valuation Allowance, Current | 12,293 | $ 17,980 |
Equity Securities [Member] |  |  |
Available-for-sale Securities, Accumulated Gross Unrealized Gain (Loss), before Tax | $ 1,800 |  |
Silver [Member] |  |  |
Metals Contained in Concentrates | oz | 1,400,000 |  |
Gold [Member] |  |  |
Metals Contained in Concentrates | oz | 4,679 |  |
Zinc [Member] |  |  |
Metals Contained in Concentrates | T | 10,166 |  |
Lead [Member] |  |  |
Metals Contained in Concentrates | T | 4,052 |  |
Minimum [Member] |  |  |
Property, Plant and Equipment, Useful Life | 1 year |  |
Maximum [Member] |  |  |
Property, Plant and Equipment, Useful Life | 22 years |  |

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