The increase in commitment fees rate on borrowings.

No definition available.

Name:	fsm_BorrowingsIncreaseInCommitmentFeesInterestRate
Namespace Prefix:	fsm_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

The increase in adjustment to the basis (reference rate) used for calculation of the interest rate on borrowings.

+ References

No definition available.

+ Details

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

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Namespace Prefix:	fsm_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

No definition available.

+ Details

Name:	fsm_IfrsGainLossOnExtinguishmentOfDebt
Namespace Prefix:	fsm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

No definition available.

+ Details

Name:	fsm_IfrsLineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	fsm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of outstanding funds that the entity is obligated to repay.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2022-03-24
-Paragraph 55
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2022-en-r&anchor=para_55&doctype=Standard
-URIDate 2022-03-24

+ Details

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

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IFRS
-Number 7
-IssueDate 2022-03-24
-Paragraph 7
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2022-en-r&anchor=para_7&doctype=Standard
-URIDate 2022-03-24

+ Details

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

- Definition

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.

+ References

No definition available.

+ Details

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

- Details

Name:	ifrs-full_RangeAxis=ifrs-full_BottomOfRangeMember
Namespace Prefix:
Data Type:	na
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Period Type:

- Details

Name:	ifrs-full_TypesOfInterestRatesAxis=fsm_LondonInterbankOfferedRateLiborMember
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Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_RangeAxis=ifrs-full_TopOfRangeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_StatementScenarioAxis=fsm_AfterThreeYearsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	ifrs-full_TypesOfInterestRatesAxis=fsm_IfrsSecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Namespace Prefix:
Data Type:	na
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DEBT - Credit Facilities (Details) $ in Thousands			12 Months Ended
DEBT - Credit Facilities (Details) $ in Thousands	Dec. 15, 2022 USD ($)	Nov. 04, 2021 USD ($)	Dec. 31, 2021 USD ($)	Dec. 14, 2022 USD ($)	Nov. 05, 2021 USD ($)
Disclosure of detailed information about borrowings [line items]
Loss on extinguishment of debt facility			$ 595
Bottom of range [member] \| London Interbank Offered Rate Libor [Member]
Disclosure of detailed information about borrowings [line items]
Borrowings, interest rate basis		two
Top of range [member] \| London Interbank Offered Rate Libor [Member]
Disclosure of detailed information about borrowings [line items]
Borrowings, interest rate basis		three
Amended Credit Facility [Member]
Disclosure of detailed information about borrowings [line items]
Debt term		4 years
Borrowing capacity	$ 250,000	$ 120,000		$ 200,000	$ 200,000
Amended Credit Facility [Member] \| After Three Years [Member]
Disclosure of detailed information about borrowings [line items]
Borrowing capacity		$ 150,000
Amended Stepped Down Credit Facility [Member]
Disclosure of detailed information about borrowings [line items]
Borrowing capacity	175,000			$ 150,000
Accordion Option [Member]
Disclosure of detailed information about borrowings [line items]
Borrowings	$ 50,000
Accordion Option [Member] \| Ifrs Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Disclosure of detailed information about borrowings [line items]
Applicable loan margins increased	0.25
Accordion Option [Member] \| Bottom of range [member]
Disclosure of detailed information about borrowings [line items]
Borrowings increase in commitment fees interest rate	0.09
Accordion Option [Member] \| Top of range [member]
Disclosure of detailed information about borrowings [line items]
Borrowings increase in commitment fees interest rate	0.12