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Reversal of Impairment (Schedule of Metal Prices Assumptions Used for Impairment Determination) (Details) | Dec. 31, 2017 $ / oz $ / T
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Silver Commodity Type [member] |
Metal Price Assumptions Used [line items] |
2018 | $ / oz | 17.56
2019 | $ / oz | 18.44
2020 | $ / oz | 19.00
2021 | $ / oz | 19.00
2022 - 2025 | $ / oz | 18.40
Gold Commodity Type [member] |
Metal Price Assumptions Used [line items] |
2018 | $ / oz | 1,300
2019 | $ / oz | 1,300
2020 | $ / oz | 1,342
2021 | $ / oz | 1,325
2022 - 2025 | $ / oz | 1,325
Lead Commodity [member] |
Metal Price Assumptions Used [line items] |
2018 | $ / T | 2,469
2019 | $ / T | 2,403
2020 | $ / T | 2,315
2021 | $ / T | 2,205
2022 - 2025 | $ / T | 2,205
Zinc Commodity [member] |
Metal Price Assumptions Used [line items] |
2018 | $ / T | 3,175
2019 | $ / T | 3,031
2020 | $ / T | 2,756
2021 | $ / T | 2,756
2022 - 2025 | $ / T | 2,425

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