Name:	gsm_IfrsDebtInstrumentTerm
Namespace Prefix:	gsm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

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

Name:	ifrs-full_Borrowings
Namespace Prefix:	ifrs-full_
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

Name:	ifrs-full_BorrowingsAdjustmentToInterestRateBasis
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Data Type:	dtr-2022:percentItemType
Balance Type:	na
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.

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The nominal or face amount of a financial instrument, used to calculate payments made on that instrument.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Note Expiry date 2027-01-01
-Name IAS
-Number 1
-IssueDate 2025-01-01
-Paragraph 112
-Subparagraph c
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2025-en-b&anchor=para_112_c&doctype=Standard
-URIDate 2025-03-27

Name:	ifrs-full_NotionalAmount
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

Name:	ifrs-full_TypesOfInterestRatesAxis=gsm_EuriborOneMonthMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	ifrs-full_BorrowingsByNameAxis=gsm_IndirectLoanFromBanquePalatineMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	ifrs-full_TypesOfInterestRatesAxis=gsm_EuriborThreeMonthMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	ifrs-full_BorrowingsByNameAxis=gsm_NewMarketsTaxCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	ifrs-full_TypesOfInterestRatesAxis=ifrs-full_FixedInterestRateMember
Namespace Prefix:
Data Type:	na
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Name:	ifrs-full_BorrowingsByNameAxis=gsm_VagalumeLoanMember
Namespace Prefix:
Data Type:	na
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Name:	ifrs-full_TypesOfInterestRatesAxis=gsm_EuriborTwelveMonthMember
Namespace Prefix:
Data Type:	na
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