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Financial Instruments and Risk Management (Gold Option Contracts) (Details) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 USD ($) $ / oz oz | Dec. 31, 2019 USD ($)
Disclosure of detailed information about hedged items [line items] |  |
Unrealized gains | $ (0.7) | $ 0.6
Gold Options [Member] | Commodity price risk [member] |  |
Disclosure of detailed information about hedged items [line items] |  |
Financial assets, at fair value |  | 0.7
Gains (losses) on change in fair value of derivatives | (8.1) | (5.9)
Unrealized gains | $ 0.7 | $ 0.6
Gold Options [Member] | 2018 [member] | Commodity price risk [member] |  |
Disclosure of detailed information about hedged items [line items] |  |
Ounces subject to contract | oz | 31,500 |
Purchase Put Options [Member] | Gold Options [Member] | 2018 [member] | Commodity price risk [member] |  |
Disclosure of detailed information about hedged items [line items] |  |
Average realized price per ounce | $ / oz | 1,730 |
Sold Call Option [Member] | Gold Options [Member] | 2018 [member] | Commodity price risk [member] |  |
Disclosure of detailed information about hedged items [line items] |  |
Average realized price per ounce | $ / oz | 2,074 |

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