XML 107 R31.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Decommissioning Liabilities (Tables) | 12 Months Ended
--- | ---
Dec. 31, 2019
Asset Retirement Obligation Disclosure1 [Abstract] |
Schedule of Change in Asset Retirement Obligation | A continuity of the decommissioning liability is as follows:
| Total
Balance – December 31, 2017 | $44.6 |
Reclamation expenditures | (0.9) |
Accretion expense | 3.0 |
Revisions to expected discounted cash flows | (1.8) |
Balance – December 31, 2018 | $44.9
Reclamation expenditures | (2.0 | )
Accretion expense | 2.8 |
Revisions to expected discounted cash flows | 13.3 |
Balance – December 31, 2019 | $59.0
Less: Current portion of decommissioning liability | (1.9) |
| $57.1

X
- Definition Asset Retirement Obligation Disclosure1 [Abstract] + References No definition available. + Details
Name: | agi_AssetRetirementObligationDisclosure1Abstract
Namespace Prefix: | agi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The disclosure of other provisions. [Refer: Other provisions] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 37 -IssueDate 2019-01-01 -Paragraph 84 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=37&code=ifrs-tx-2019-en-r&anchor=para_84&doctype=Standard -URIDate 2019-03-27 + Details
Name: | ifrs-full_DisclosureOfOtherProvisionsExplanatory
Namespace Prefix: | ifrs-full_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration