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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Threshold amount of default on payment obligations of commercial (non-financial) nature assumed with third parties for individual or cumulative amount.

No definition available.

Name:	gsm_DebtInstrumentThresholdAmountOfDefaultOnPaymentObligationsOnCommercialNonFinancialNature
Namespace Prefix:	gsm_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Threshold amount of default on payment obligations arising from indebtedness contracted with creditors during the period.

No definition available.

Name:	gsm_DebtInstrumentThresholdAmountOfDefaultOnPaymentObligationsWithCreditors
Namespace Prefix:	gsm_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

The exception to restriction of payment of intercompany net commercial balance as of 30 June 2021.

No definition available.

Name:	gsm_ExceptionToRestrictionOfPaymentOfIntercompanyNetCommercialBalanceAsOfJune302021
Namespace Prefix:	gsm_
Data Type:	xbrli:monetaryItemType
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Percentage of ownership interest ceases to exist that result in change of control causing early repayment of loan.

No definition available.

Name:	gsm_PercentageOfOwnershipInterestCeasesToExistTriggersEarlyRepaymentOfLoan
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Data Type:	dtr-types:percentItemType
Balance Type:	na
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The amount of outstanding funds that the entity is obligated to repay.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Note Expiry date 2027-01-01
-Name IAS
-Number 1
-IssueDate 2025-01-01
-Paragraph 55
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2025-en-b&anchor=para_55&doctype=Standard
-URIDate 2025-03-27

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The adjustment to the basis (reference rate) used for calculation of the interest rate on borrowings. [Refer: Borrowings]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IFRS
-Number 7
-IssueDate 2025-01-01
-Paragraph 7
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2025-en-r&anchor=para_7&doctype=Standard
-URIDate 2025-03-27

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Period Type:	instant

The interest rate on borrowings. [Refer: Borrowings]

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Namespace Prefix:	ifrs-full_
Data Type:	dtr-2022:percentItemType
Balance Type:	na
Period Type:	instant

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table.

No definition available.

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

The fair value of financial liabilities. [Refer: At fair value [member]; Financial liabilities]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2025-01-01
-Paragraph 25
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2025-en-r&anchor=para_25&doctype=Standard
-URIDate 2025-03-27

Name:	ifrs-full_FinancialLiabilitiesAtFairValue
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The amount of assistance by government in the form of transfers of resources to an entity in return for past or future compliance with certain conditions relating to the operating activities of the entity, recognised as deferred income. They exclude those forms of government assistance that cannot reasonably have a value placed upon them and transactions with government that cannot be distinguished from the normal trading transactions of the entity. [Refer: Deferred income other than contract liabilities; Government [member]]

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The cash outflow to settle borrowings, classified as financing activities. [Refer: Borrowings]

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 7
-IssueDate 2025-01-01
-Paragraph 17
-Subparagraph d
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=7&code=ifrs-tx-2025-en-r&anchor=para_17_d&doctype=Standard
-URIDate 2025-03-27

Name:	ifrs-full_RepaymentsOfBorrowingsClassifiedAsFinancingActivities
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Name:	ifrs-full_BorrowingsByNameAxis=gsm_SepiLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_SignificantInvestmentsInSubsidiariesAxis=gsm_FerroglobePlcInterestInGroupoFerroatlanticaAndGrupoFerroatlanticaDeServiciosMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_SignificantInvestmentsInSubsidiariesAxis=gsm_GrupoVillarMirSauVotingStakeInFerroglobePlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_SignificantInvestmentsInSubsidiariesAxis=gsm_FgSpainDirectOrIndirectInterestInFgCorporateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_SignificantInvestmentsInSubsidiariesAxis=gsm_GrupoFerroatlnticaS.a.u.AndGrupoFerrotlanticaDeServiciosS.l.u.Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_LevelsOfFairValueHierarchyAxis=ifrs-full_Level2OfFairValueHierarchyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_ValuationTechniquesUsedInFairValueMeasurementAxis=ifrs-full_DiscountedCashFlowMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_TypesOfInterestRatesAxis=ifrs-full_FixedInterestRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_TypesOfInterestRatesAxis=ifrs-full_FloatingInterestRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	gsm_InstallmentAxis=gsm_InterestRateSpreadFirstYearMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	gsm_InstallmentAxis=gsm_InterestRateSpreadSecondAndThirdYearsMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	gsm_InstallmentAxis=gsm_InterestRateSpreadFourthYearMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	gsm_InstallmentAxis=gsm_InterestRateSpreadAdditionalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_MaturityAxis=gsm_LoanMaturingInFebruary2025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: