XML 95 R63.htm IDEA: XBRL DOCUMENT v3.21.1

Share Capital (Schedule of Stock Options Range for Outstanding and Exercisable Shares) (Details)	12 Months Ended
	Dec. 31, 2020 shares $ / shares	Dec. 31, 2019 shares $ / shares	Dec. 31, 2018 shares $ / shares
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options outstanding (in shares) | shares	3,476,579	4,465,262	6,655,455
Outstanding weighted average exercise price (CAD per share)	$ 6.80	$ 6.59	$ 7.38
Weighted average remaining contractual life of options outstanding (years)	4 years 4 months 20 days
Number of options exercisable (in shares) | shares	1,722,702
Exercisable weighted average exercise price (CAD per share))	$ 6.51
$3.01 - $5.00
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options outstanding (in shares) | shares	560,000
Outstanding weighted average exercise price (CAD per share)	$ 3.75
Weighted average remaining contractual life of options outstanding (years)	2 years 18 days
Number of options exercisable (in shares) | shares	560,000
Exercisable weighted average exercise price (CAD per share))	$ 3.75
$6.01 - $7.00
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options outstanding (in shares) | shares	1,596,265
Outstanding weighted average exercise price (CAD per share)	$ 6.57
Weighted average remaining contractual life of options outstanding (years)	4 years 8 months 15 days
Number of options exercisable (in shares) | shares	679,852
Exercisable weighted average exercise price (CAD per share))	$ 6.57
$7.01 - $8.00
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options outstanding (in shares) | shares	809,184
Outstanding weighted average exercise price (CAD per share)	$ 7.62
Weighted average remaining contractual life of options outstanding (years)	6 years 7 days
Number of options exercisable (in shares) | shares	291
Exercisable weighted average exercise price (CAD per share))	$ 7.07
$8.01 - $9.00
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options outstanding (in shares) | shares	28,571
Outstanding weighted average exercise price (CAD per share)	$ 8.63
Weighted average remaining contractual life of options outstanding (years)	6 years 1 month 28 days
Number of options exercisable (in shares) | shares	0
Exercisable weighted average exercise price (CAD per share))	$ 0
$9.01 - $10.00
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Number of options outstanding (in shares) | shares	482,559
Outstanding weighted average exercise price (CAD per share)	$ 9.62
Weighted average remaining contractual life of options outstanding (years)	3 years 2 months 4 days
Number of options exercisable (in shares) | shares	482,559
Exercisable weighted average exercise price (CAD per share))	$ 9.62
Bottom of range [member] | $3.01 - $5.00
Disclosure of range of exercise prices of outstanding share options [line items]
Exercise price of outstanding share options	3.01
Bottom of range [member] | $6.01 - $7.00
Disclosure of range of exercise prices of outstanding share options [line items]
Exercise price of outstanding share options	7.01
Bottom of range [member] | $7.01 - $8.00
Disclosure of range of exercise prices of outstanding share options [line items]
Exercise price of outstanding share options	11.01
Top of range [member] | $3.01 - $5.00
Disclosure of range of exercise prices of outstanding share options [line items]
Exercise price of outstanding share options	7.00
Top of range [member] | $6.01 - $7.00
Disclosure of range of exercise prices of outstanding share options [line items]
Exercise price of outstanding share options	11.00
Top of range [member] | $7.01 - $8.00
Disclosure of range of exercise prices of outstanding share options [line items]
Exercise price of outstanding share options	$ 19.00

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_DisclosureOfNumberAndWeightedAverageRemainingContractualLifeOfOutstandingShareOptionsLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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_DisclosureOfRangeOfExercisePricesOfOutstandingShareOptionsLineItems
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The exercise price of outstanding share options.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2020-01-01
-Paragraph 45
-Subparagraph d
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=2&code=ifrs-tx-2020-en-r&anchor=para_45_d&doctype=Standard
-URIDate 2020-01-01

+ Details

Name:	ifrs-full_ExercisePriceOfOutstandingShareOptions2019
Namespace Prefix:	ifrs-full_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The number of share options outstanding in a share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2020-01-01
-Paragraph 45
-Subparagraph d
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=2&code=ifrs-tx-2020-en-r&anchor=para_45_d&doctype=Standard
-URIDate 2020-01-01

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2020-01-01
-Paragraph 45
-Subparagraph b
-Clause i
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=2&code=ifrs-tx-2020-en-r&anchor=para_45_b_i&doctype=Standard
-URIDate 2020-01-01

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2020-01-01
-Paragraph 45
-Subparagraph b
-Clause vi
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=2&code=ifrs-tx-2020-en-r&anchor=para_45_b_vi&doctype=Standard
-URIDate 2020-01-01

+ Details

Name:	ifrs-full_NumberOfOutstandingShareOptions
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The number of share options exercisable in a share-based payment arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2020-01-01
-Paragraph 45
-Subparagraph b
-Clause vii
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=2&code=ifrs-tx-2020-en-r&anchor=para_45_b_vii&doctype=Standard
-URIDate 2020-01-01

+ Details

Name:	ifrs-full_NumberOfShareOptionsExercisableInSharebasedPaymentArrangement
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The weighted average exercise price of share options exercisable in a share-based payment arrangement. [Refer: Weighted average [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2020-01-01
-Paragraph 45
-Subparagraph b
-Clause vii
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=2&code=ifrs-tx-2020-en-r&anchor=para_45_b_vii&doctype=Standard
-URIDate 2020-01-01

+ Details

Name:	ifrs-full_WeightedAverageExercisePriceOfShareOptionsExercisableInSharebasedPaymentArrangement2019
Namespace Prefix:	ifrs-full_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The weighted average exercise price of share options outstanding in a share-based payment arrangement. [Refer: Weighted average [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2020-01-01
-Paragraph 45
-Subparagraph b
-Clause i
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=2&code=ifrs-tx-2020-en-r&anchor=para_45_b_i&doctype=Standard
-URIDate 2020-01-01

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2020-01-01
-Paragraph 45
-Subparagraph b
-Clause vi
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=2&code=ifrs-tx-2020-en-r&anchor=para_45_b_vi&doctype=Standard
-URIDate 2020-01-01

+ Details

Name:	ifrs-full_WeightedAverageExercisePriceOfShareOptionsOutstandingInSharebasedPaymentArrangement2019
Namespace Prefix:	ifrs-full_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The weighted average remaining contractual life of outstanding share options. [Refer: Weighted average [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2020-01-01
-Paragraph 45
-Subparagraph d
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=2&code=ifrs-tx-2020-en-r&anchor=para_45_d&doctype=Standard
-URIDate 2020-01-01

+ Details

Name:	ifrs-full_WeightedAverageRemainingContractualLifeOfOutstandingShareOptions2019
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis=agi_ExercisePriceRangeOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis=agi_ExercisePriceRangeTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis=agi_ExercisePriceRangeThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis=agi_ExercisePriceRangeFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_RangesOfExercisePricesForOutstandingShareOptionsAxis=agi_ExercisePriceRangeFiveMember
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: