XML 113 R82.htm IDEA: XBRL DOCUMENT
v3.19.1

Financial Instruments and Risk Management (Unrealized Gains (Losses) on Foreign Currency Contracts) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Disclosure of detailed information about hedged items [line items] |  |
Unrealized gains | $ 0.4 | $ 0.3

X
- Definition Unrealized Gain (Loss) on Derivatives1 + References No definition available. + Details
Name: | agi_UnrealizedGainLossonDerivatives1
Namespace Prefix: | agi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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_DisclosureOfDetailedInformationAboutHedgedItemsLineItems
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration