XML 72 R56.htm IDEA: XBRL DOCUMENT
v3.20.4

Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
--- | --- | --- | ---
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Non-capital losses carried forward | $ (559.9) | $ (513.7) |
Deferred income tax liability | 559.9 | 513.7 | $ 491.5
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 | 591.8 | 557.0 |
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 | 8.8 | 7.9 |
Other taxable temporary differences |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Non-capital losses carried forward | (25.5) | (19.8) |
Non-capital losses carried forward |  |  |
Disclosure of temporary difference, unused tax losses and unused tax credits [line items] |  |  |
Non-capital losses carried forward | $ (15.2) | $ (31.4) |

X
- 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 2020-01-01 -Paragraph 81 -Subparagraph g -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2020-en-r&anchor=para_81_g_i&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 54 -Subparagraph o -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_54_o&doctype=Standard -URIDate 2020-01-01 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 56 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_56&doctype=Standard -URIDate 2020-01-01 + Details
Name: | ifrs-full_DeferredTaxAssets
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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 2020-01-01 -Paragraph 81 -Subparagraph g -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2020-en-r&anchor=para_81_g_i&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 54 -Subparagraph o -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_54_o&doctype=Standard -URIDate 2020-01-01 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 56 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_56&doctype=Standard -URIDate 2020-01-01 + Details
Name: | ifrs-full_DeferredTaxLiabilities
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The amount of deferred tax liabilities or assets. [Refer: Deferred tax liabilities; Deferred tax assets] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 12 -IssueDate 2020-01-01 -Paragraph 81 -Subparagraph g -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2020-en-r&anchor=para_81_g_i&doctype=Standard -URIDate 2020-01-01 + Details
Name: | ifrs-full_DeferredTaxLiabilityAsset
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
Name: | ifrs-full_DisclosureOfTemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsLineItems
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis=agi_MineralPropertyPlantandEquipmentInExcessofTaxValueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis=agi_InventoriesInExcessofTaxValueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis=ifrs-full_OtherTemporaryDifferencesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TemporaryDifferenceUnusedTaxLossesAndUnusedTaxCreditsAxis=ifrs-full_UnusedTaxLossesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |