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Income Taxes - Significant components of unrecognized deferred tax assets (Details) - CAD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
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Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Unrecognized deferred tax assets | $ 433,034 | $ 401,853
Income tax losses [member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Unrecognized deferred tax assets | 270,154 | 259,770
Property, plant and equipment, deferred tax assets [Member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Unrecognized deferred tax assets | 2,344 | 2,076
Provision for reclamation [member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Unrecognized deferred tax assets | 88,036 | 71,463
Long-term investments and other, deferred tax assets [member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Unrecognized deferred tax assets | $ 72,500 | $ 68,544

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