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Financial Instruments and Risk Management (Gold Option Contracts) (Details) $ in Millions |  | 12 Months Ended
--- | --- | ---
Jan. 07, 2019 USD ($) | Dec. 31, 2019 USD ($) $ / oz oz | Dec. 31, 2018 USD ($)
Disclosure of detailed information about hedged items [line items] |  |  |
Gains (losses) on change in fair value of derivatives | $ 3.9 |  |
Unrealized gains |  | $ 0.6 | $ 0.4
Gold Options [Member] | Commodity price risk [member] |  |  |
Disclosure of detailed information about hedged items [line items] |  |  |
Financial assets, at fair value |  | 0.7 | 0.1
Gains (losses) on change in fair value of derivatives |  | (5.9) | (3.9)
Unrealized gains |  | $ 6.5 | $ 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 |  | 70,050 |
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 |  | 1,420 |
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 |  | 1,658 |

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