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Income Taxes - Significant components of deferred tax assets and liabilities (Details) - CAD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Net deferred tax asset, recognized in earnings | $ (52,330) | $ 147,091 |
Deferred tax assets | 956,376 | 1,006,012 |
Deferred tax liabilities | 0 | 0 |
Net deferred tax asset | 956,376 | 1,006,012 | $ 848,704
Property, plant and equipment [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Net deferred tax asset, recognized in earnings | 74,039 | 119,132 |
Net deferred tax assets | 319,185 | 245,206 |
Provision for reclamation [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Net deferred tax asset, recognized in earnings | 2,325 | (36,622) |
Net deferred tax assets | 193,514 | 191,189 |
Inventories [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Net deferred tax asset, recognized in earnings | (2,163) | 1,137 |
Net deferred tax assets | 0 | 2,163 |
Net deferred tax liabilities | 301 | 0 |
Foreign exploration and development [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Net deferred tax asset, recognized in earnings | (14) | (14) |
Net deferred tax assets | 5,267 | 5,281 |
Income tax losses (gains) [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Net deferred tax asset, recognized in earnings | (108,839) | 39,289 |
Net deferred tax assets | 390,341 | 499,180 |
Defined benefit plan actuarial losses [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Net deferred tax asset, recognized in earnings | 0 | 0 |
Net deferred tax assets | 7,947 | 5,646 |
Long-term investments and other, deferred tax assets [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Net deferred tax asset, recognized in earnings | (17,377) | 24,169 |
Net deferred tax assets | 40,423 | 57,347 |
Deferred tax assets [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Net deferred tax asset, recognized in earnings | (52,029) | 147,091 |
Net deferred tax assets | 956,677 | 1,006,012 |
Inventories [member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Net deferred tax asset, recognized in earnings | 301 | 0 |
Deferred tax liabilities [Member] |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Net deferred tax asset, recognized in earnings | 301 | 0 |
Net deferred tax liabilities | $ 301 | $ 0 |

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- Definition The amounts of income taxes recoverable in future periods in respect of: (a) deductible temporary differences; (b) the carryforward of unused tax losses; and (c) the carryforward of unused tax credits. [Refer: Temporary differences [member]; Unused tax credits [member]; Unused tax losses [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2019-01-01 -Paragraph 81 -Subparagraph g -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_81_g_i&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 54 -Subparagraph o -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_54_o&doctype=Standard -URIDate 2019-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 56 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_56&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The amount of tax expense or income relating to changes in deferred tax liabilities and deferred tax assets, recognised in profit or loss. [Refer: Deferred tax assets; Deferred tax expense (income); Deferred tax liabilities] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2019-01-01 -Paragraph 81 -Subparagraph g -Clause ii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_81_g_ii&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The amounts of income taxes payable in future periods in respect of taxable temporary differences. [Refer: Temporary differences [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2019-01-01 -Paragraph 81 -Subparagraph g -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_81_g_i&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 54 -Subparagraph o -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_54_o&doctype=Standard -URIDate 2019-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 56 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_56&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The amount of deferred tax assets net of deferred tax liabilities, when the absolute amount of deferred tax assets is greater than the absolute amount of deferred tax liabilities. [Refer: Deferred tax assets; Deferred tax liabilities] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 12 -IssueDate 2019-01-01 -Paragraph 81 -Subparagraph g -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_81_g_i&doctype=Standard -URIDate 2019-03-27 + Details
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