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Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
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Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Non-capital losses carried forward | $ (491.5) | $ (477.0) |
Deferred income tax liability | 491.5 | 477.0 | $ 291.0
Accounting value of mineral property, plant and equipment in excess of tax value |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Deferred tax assets | 446.8 | 409.0 |
Accounting value of inventories in excess of tax value |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Deferred tax assets | 13.8 | 34.7 |
Other taxable temporary differences |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Deferred tax assets | 64.3 | 58.6 |
Non-capital losses carried forward |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Non-capital losses carried forward | $ (33.4) | $ (25.3) |

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