XML 78 R47.htm IDEA: XBRL DOCUMENT
v3.19.1

Inventory (Narrative) (Details) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 USD ($) oz | Dec. 31, 2017 USD ($)
Inventory [Line Items] |  |
Long-term inventory | $ 30.0 | $ 68.7
Mining and processing costs, inventories | 393.1 | 323.3
Amortization costs, Inventories | 166.6 | $ 125.6
El Chanate [Member] |  |
Inventory [Line Items] |  |
Inventory write-down | $ 64.0 |
Unrecoverable Ounces | oz | 51,900 |
Impairment loss | $ 64.0 |
Impairment loss net of tax | 49.9 |
El Chanate [Member] | Mining [Member] |  |
Inventory [Line Items] |  |
Inventory write-down | 62.5 |
El Chanate [Member] | Amortization [Member] |  |
Inventory [Line Items] |  |
Inventory write-down | $ 1.5 |

X
- Definition Amortization Costs, Inventories + References No definition available. + Details
Name: | agi_AmortizationCostsInventories
Namespace Prefix: | agi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Impairment Loss Net of Tax + References No definition available. + Details
Name: | agi_ImpairmentLossNetofTax
Namespace Prefix: | agi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition [Line Items] for Inventory [Table] + References No definition available. + Details
Name: | agi_Inventory1LineItems
Namespace Prefix: | agi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Mining and Processing Costs, Inventories + References No definition available. + Details
Name: | agi_MiningandProcessingCostsInventories
Namespace Prefix: | agi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Unrecoverable Ounces + References No definition available. + Details
Name: | agi_UnrecoverableOunces
Namespace Prefix: | agi_
Data Type: | num:massItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount recognised as a reduction of the carrying amount of an asset or cash-generating unit to its recoverable amount. [Refer: Carrying amount [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2018-01-01 -Paragraph 130 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2018-03-01&anchor=para_130_b&doctype=Standard -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2018-01-01 -Paragraph 130 -Subparagraph d -Clause ii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=36&date=2018-03-01&anchor=para_130_d_ii&doctype=Standard -URIDate 2018-03-16 + Details
Name: | ifrs-full_ImpairmentLoss
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The amount of expense recognised related to the write-down of inventories to net realisable value. [Refer: Inventories] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 2 -IssueDate 2018-01-01 -Paragraph 36 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=2&date=2018-03-01&anchor=para_36_e&doctype=Standard -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 98 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_98_a&doctype=Standard -URIDate 2018-03-16 + Details
Name: | ifrs-full_InventoryWritedown2011
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount of non-current inventories. [Refer: Inventories] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 54 -Subparagraph g -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_54_g&doctype=Standard -URIDate 2018-03-16 + Details
Name: | ifrs-full_NoncurrentInventories
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis=agi_ElChanateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | agi_InventoryAxis=agi_MiningMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | agi_InventoryAxis=agi_AmortizationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |