XML 59 R27.htm IDEA: XBRL DOCUMENT
v3.21.1

Amounts Receivable (Tables) | 12 Months Ended
--- | ---
Dec. 31, 2020
Subclassifications of assets, liabilities and equities [abstract] |
Schedule of Receivables |
| December 31, 2020 | December 31, 2019
Sales tax receivables |  |
Canada | $5.4 |  | $8.9 |
Mexico | 17.7 |  | 18.1 |
Other | 4.0 |  | 5.7 |
Other receivables | 7.6 |  | 4.7 |
| $34.7 |  | $37.4 |

X
- Definition Schedule of Receivables [Table Text Block] + References No definition available. + Details
Name: | agi_ScheduleofReceivablesTableTextBlock
Namespace Prefix: | agi_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | ifrs-full_SubclassificationsOfAssetsLiabilitiesAndEquitiesAbstract
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration