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Note 10 - Derivative Instruments (Tables) | 12 Months Ended
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Dec. 31, 2017
Notes Tables |
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] |
December 31, 2017 |  | Ounces/pounds under contract (in 000's) |  |  | Average price per ounce/pound |
|  | Silver |  |  | Gold |  |  | Zinc |  |  | Lead |  |  | Silver |  |  | Gold |  |  | Zinc |  |  | Lead |
|  | (ounces) |  |  | (ounces) |  |  | (pounds) |  |  | (pounds) |  |  | (ounces) |  |  | (ounces) |  |  | (pounds) |  |  | (pounds) |
Contracts on provisional sales |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2018 settlements |  |  | 1,447 |  |  |  | 5 |  |  |  | 21,550 |  |  |  | 4,740 |  |  | $ | 16.64 |  |  | $ | 1,279 |  |  | $ | 1.45 |  |  | $ | 1.11 |
Contracts on forecasted sales |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2018 settlements |  |  | — |  |  |  | — |  |  |  | 32,187 |  |  |  | 16,645 |  |  |  | N/A |  |  |  | N/A |  |  | $ | 1.29 |  |  | $ | 1.06 |
2019 settlements |  |  | — |  |  |  | — |  |  |  | 23,589 |  |  |  | 18,078 |  |  |  | N/A |  |  |  | N/A |  |  | $ | 1.33 |  |  | $ | 1.09 |
2020 settlements |  |  | — |  |  |  | — |  |  |  | 3,307 |  |  |  | 2,866 |  |  |  | N/A |  |  |  | N/A |  |  | $ | 1.27 |  |  | $ | 1.08 |
December 31, 2016 |  | Ounces/pounds under contract (in 000's) |  |  | Average price per ounce/pound |
|  | Silver |  |  | Gold |  |  | Zinc |  |  | Lead |  |  | Silver |  |  | Gold |  |  | Zinc |  |  | Lead |
|  | (ounces) |  |  | (ounces) |  |  | (pounds) |  |  | (pounds) |  |  | (ounces) |  |  | (ounces) |  |  | (pounds) |  |  | (pounds) |
Contracts on provisional sales |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2017 settlements |  |  | 1,295 |  |  |  | 4 |  |  |  | 19,070 |  |  |  | 7,441 |  |  | $ | 16.29 |  |  | $ | 1,172 |  |  | $ | 1.18 |  |  | $ | 0.97 |
Contracts on forecasted sales |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2017 settlements |  |  | N/A |  |  |  | N/A |  |  |  | 35,384 |  |  |  | 17,637 |  |  |  | N/A |  |  |  | N/A |  |  | $ | 1.19 |  |  | $ | 1.03 |
2018 settlements |  |  | N/A |  |  |  | N/A |  |  |  | 13,779 |  |  |  | 5,732 |  |  |  | N/A |  |  |  | N/A |  |  | $ | 1.21 |  |  | $ | 1.05 |

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- Definition Tabular disclosure of the notional amounts of outstanding derivative positions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959 + Details
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