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Income Taxes - Significant components of unrecognized deferred tax assets (Details) - CAD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
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Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Unrecognized deferred tax assets | $ 428,113 | $ 433,034
Income tax losses (gains) [member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Unrecognized deferred tax assets | 280,330 | 270,154
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 | 2,321 | 2,344
Provision for reclamation [member] |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |
Unrecognized deferred tax assets | 75,082 | 88,036
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 | $ 70,380 | $ 72,500

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