XML 66 R34.htm IDEA: XBRL DOCUMENT v3.21.1

Other (Loss) Gain (Tables)

12 Months Ended

Dec. 31, 2020

Other Gain (Loss) [Abstract]

Schedule of Other Nonoperating Income (Expense)

Other (loss) gain recorded in net earnings for the years ended:

									December 31,			December 31,
									2020			2019
Reduction of obligation to renounce flow-through exploration expenditures									$1.0			$0.6
Unrealized gain (loss) on non-hedging derivatives									0.7			(0.6)
Loss on disposal of assets									(1.0)			(0.7)
Gain on sale of non-core royalties									0.6			8.0
Other									(5.0)			(2.2)
									($3.7)			$5.1

X

- Definition

Other Gain (Loss) [Abstract]

+ References

No definition available.

+ Details

Name:	agi_OtherGainLossAbstract
Namespace Prefix:	agi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Schedule of Other Nonoperating Income (Expense)1 [Table Text Block]

+ References

No definition available.

+ Details

Name:	agi_ScheduleofOtherNonoperatingIncomeExpense1TableTextBlock
Namespace Prefix:	agi_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration