XML 94 R78.htm IDEA: XBRL DOCUMENT
v3.20.4

Financial Instruments and Risk Management (Currency Contracts) (Details) $ in Millions, $ in Millions, $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($) | Dec. 31, 2020 CAD ($) | Dec. 31, 2020 $ / $ | Dec. 31, 2020 MXN ($) | Dec. 31, 2020 $ / $
Collars and Forwards [Member] |  |  |  |  |  |
Disclosure of detailed information about hedged items [line items] |  |  |  |  |  |
Financial liabilities, at fair value |  | $ 3.3 |  |  |  |
Gains (losses) on change in fair value of derivatives | $ 1.4 | $ (1.5) |  |  |  |
2019 [member] | Collars [Member] | Currency risk [member] |  |  |  |  |  |
Disclosure of detailed information about hedged items [line items] |  |  |  |  |  |
Notional amount |  |  | $ 45.0 |  | $ 1,185.0 |
Bottom of range [member] | 2019 [member] | Collars [Member] | Currency risk [member] |  |  |  |  |  |
Disclosure of detailed information about hedged items [line items] |  |  |  |  |  |
Average rate of hedging instrument |  |  |  | 131.00% |  | 2096.00%
Top of range [member] | 2019 [member] | Collars [Member] | Currency risk [member] |  |  |  |  |  |
Disclosure of detailed information about hedged items [line items] |  |  |  |  |  |
Average rate of hedging instrument |  |  |  | 138.00% |  | 2528.00%

X
- Definition The average rate of a hedging instrument. [Refer: Hedging instruments [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2020-01-01 -Paragraph 23B -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2020-en-r&anchor=para_23B_b&doctype=Standard -URIDate 2020-01-01 + Details
Name: | ifrs-full_AverageRateOfHedgingInstrument
Namespace Prefix: | ifrs-full_
Data Type: | num:percentItemType
Balance Type: | na
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_DisclosureOfDetailedInformationAboutHedgedItemsLineItems
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The fair value of financial liabilities. [Refer: At fair value [member]; Financial liabilities] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2020-01-01 -Paragraph 25 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2020-en-r&anchor=para_25&doctype=Standard -URIDate 2020-01-01 + Details
Name: | ifrs-full_FinancialLiabilitiesAtFairValue
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The gains (losses) resulting from change in the fair value of derivatives recognised in profit or loss. [Refer: Derivatives [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 85 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_85&doctype=Standard -URIDate 2020-01-01 + Details
Name: | ifrs-full_GainsLossesOnChangeInFairValueOfDerivatives
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The nominal or face amount of a financial instrument, used to calculate payments made on that instrument. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2020-01-01 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_112_c&doctype=Standard -URIDate 2020-01-01 + Details
Name: | ifrs-full_NotionalAmount
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | ifrs-full_HedgingInstrumentsAxis=agi_CollarsandForwardsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_MaturityAxis=ifrs-full_LaterThanTwoYearsAndNotLaterThanThreeYearsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_HedgingInstrumentsAxis=agi_CollarsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_TypesOfRisksAxis=ifrs-full_CurrencyRiskMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_RangeAxis=ifrs-full_BottomOfRangeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | ifrs-full_RangeAxis=ifrs-full_TopOfRangeMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |