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Financial Instruments and Risk Management (Fair Value And Presentation in the Balance Sheet) (Details) - USD ($) $ in Millions | Dec. 31, 2017 | Dec. 31, 2016
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Disclosure of detailed information about financial instruments [line items] |  |
Financial assets, at fair value | $ 0.4 |
Financial liabilities, at fair value |  | $ (2.4)
Derivatives [member] | Currency Hedging Derivative Instruments [Member] |  |
Disclosure of detailed information about financial instruments [line items] |  |
Financial assets, at fair value | 5.0 | 0.0
Derivatives [member] | Gold Options [Member] |  |
Disclosure of detailed information about financial instruments [line items] |  |
Financial assets, at fair value | 0.5 | 3.3
Derivatives [member] | Currency Derivative Instruments [Member] |  |
Disclosure of detailed information about financial instruments [line items] |  |
Financial assets, at fair value | 0.0 |
Financial liabilities, at fair value |  | 3.3
Derivatives [member] | Share Purchase Warrants [Member] |  |
Disclosure of detailed information about financial instruments [line items] |  |
Financial liabilities, at fair value | $ (0.1) | $ (2.4)

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