The cost related to the issuance of shares.

No definition available.

Name:	fmst_CostOfIssuanceOfShares
Namespace Prefix:	fmst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of government grant agreement.

+ References

No definition available.

+ Details

Name:	fmst_GovernmentGrantAgreement
Namespace Prefix:	fmst_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount fo increase (decrease) in equity for purchase of evaluation and exploration assets.

+ References

No definition available.

+ Details

Name:	fmst_IncreaseDecreaseForPurchaseOfEvaluationAndExplorationAssets
Namespace Prefix:	fmst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The increase (decrease) in the number of shares outstanding from acquisitions.

+ References

No definition available.

+ Details

Name:	fmst_IncreaseDecreaseInNumberOfSharesOutstandingAcquisitions
Namespace Prefix:	fmst_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of net smelter royalty return.

+ References

No definition available.

+ Details

Name:	fmst_NetSmelterRoyaltyReturnPercentage
Namespace Prefix:	fmst_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of cash payment for option agreement.

+ References

No definition available.

+ Details

Name:	fmst_OptionAgreementCashPayment
Namespace Prefix:	fmst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage of net smelter royalty in option agreement.

+ References

No definition available.

+ Details

Name:	fmst_OptionAgreementNetSmelterRoyaltyPercentage
Namespace Prefix:	fmst_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

Name:	fmst_Statement1LineItems
Namespace Prefix:	fmst_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of transfer agent and filing fees.

+ References

No definition available.

+ Details

Name:	fmst_TransferAgentAndFilingFees
Namespace Prefix:	fmst_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of future capital expenditures that the entity is committed to make.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2024-01-01
-Paragraph 112
-Subparagraph c
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2024-en-r&anchor=para_112_c&doctype=Standard
-URIDate 2024-03-27

+ Details

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

- Definition

The fair value, at acquisition date, of cash transferred as consideration in a business combination. [Refer: Total for all business combinations [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 3
-IssueDate 2024-01-01
-Paragraph B64
-Subparagraph f
-Clause i
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=3&code=ifrs-tx-2024-en-r&anchor=para_B64_f_i&doctype=Appendix&subtype=B
-URIDate 2024-03-27

+ Details

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

- Definition

The fair value, at the acquisition date, of equity interests of the acquirer transferred as consideration in a business combination. [Refer: Total for all business combinations [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 3
-IssueDate 2024-01-01
-Paragraph B64
-Subparagraph f
-Clause iv
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=3&code=ifrs-tx-2024-en-r&anchor=para_B64_f_iv&doctype=Appendix&subtype=B
-URIDate 2024-03-27

+ Details

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

- Definition

The amount of expense arising from the search for mineral resources, including minerals, oil, natural gas and similar non-regenerative resources after the entity has obtained legal rights to explore in a specific area, as well as the determination of the technical feasibility and commercial viability of extracting the mineral resource.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 6
-IssueDate 2024-01-01
-Paragraph 24
-Subparagraph b
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=6&code=ifrs-tx-2024-en-r&anchor=para_24_b&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_ExpenseArisingFromExplorationForAndEvaluationOfMineralResources
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The increase (decrease) in equity resulting from the acquisition of subsidiaries. [Refer: Total for all subsidiaries [member]]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2024-01-01
-Paragraph 106
-Subparagraph d
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=1&code=ifrs-tx-2024-en-r&anchor=para_106_d&doctype=Standard
-URIDate 2024-03-27

+ Details

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

- Definition

The number of instruments or interests issued or issuable at acquisition date for equity interests of the acquirer transferred as consideration in a business combination.

+ References

+ Details

Name:	ifrs-full_NumberOfInstrumentsOrInterestsIssuedOrIssuable
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

The cash outflow for expenses incurred by an entity in connection with the exploration for, and evaluation of, mineral resources before the technical feasibility and commercial viability of extracting a mineral resource are demonstrable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 7
-IssueDate 2024-01-01
-Paragraph 14
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=7&code=ifrs-tx-2024-en-r&anchor=para_14&doctype=Standard
-URIDate 2024-03-27

+ Details

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

- Definition

The cash inflow from government grants, classified as financing activities. [Refer: Government [member]; Government grants]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 20
-IssueDate 2024-01-01
-Paragraph 28
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=20&code=ifrs-tx-2024-en-r&anchor=para_28&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_ProceedsFromGovernmentGrantsClassifiedAsFinancingActivities
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The proportion of ownership interest in an associate attributable to the entity. [Refer: Total for all associates [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 27
-IssueDate 2024-01-01
-Paragraph 17
-Subparagraph b
-Clause iii
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=27&code=ifrs-tx-2024-en-r&anchor=para_17_b_iii&doctype=Standard
-URIDate 2024-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 27
-IssueDate 2024-01-01
-Paragraph 16
-Subparagraph b
-Clause iii
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=27&code=ifrs-tx-2024-en-r&anchor=para_16_b_iii&doctype=Standard
-URIDate 2024-03-27

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 12
-IssueDate 2024-01-01
-Paragraph 21
-Subparagraph a
-Clause iv
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=12&code=ifrs-tx-2024-en-r&anchor=para_21_a_iv&doctype=Standard
-URIDate 2024-03-27

+ Details

Name:	ifrs-full_ProportionOfOwnershipInterestInAssociate
Namespace Prefix:	ifrs-full_
Data Type:	dtr-2022:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash outflow for the purchase of exploration and evaluation assets. [Refer: Exploration and evaluation assets [member]]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 7
-IssueDate 2024-01-01
-Paragraph 16
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=7&code=ifrs-tx-2024-en-r&anchor=para_16&doctype=Standard
-URIDate 2024-03-27

+ Details

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

- Details

Name:	ifrs-full_SignificantInvestmentsInAssociatesAxis=fmst_ForemostMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=fmst_DenisonMinesCorpMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_NonadjustingEventsAfterReportingPeriodAxis=ifrs-full_MajorPurchasesOfAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis=fmst_JeanLakePropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis=fmst_GrassRiverPropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis=fmst_JolLithiumPropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis=fmst_PegNorthPropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis=fmst_LacSimardSouthPropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis=fmst_AthabascaPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_AttributionOfExpensesByNatureToTheirFunctionAxis=fmst_FindersAndAdvisoryFeesMember
Namespace Prefix:
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_ClassesOfPropertyPlantAndEquipmentAxis=fmst_HatchetLakeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfAssetsAxis=fmst_ManitobaGrantMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_ClassesOfPropertyPlantAndEquipmentAxis=fmst_JeanLakeAndZoroLithiumPropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 7 - Exploration and Evaluation Assets (Details Textual)											12 Months Ended					45 Months Ended	56 Months Ended	62 Months Ended
	Oct. 05, 2030	Oct. 04, 2030 CAD ($)	Oct. 04, 2027 CAD ($)	Jun. 28, 2027 CAD ($)	Jun. 28, 2026 CAD ($)	Jun. 28, 2025 CAD ($)	Jun. 28, 2024 CAD ($)	Jun. 28, 2023 CAD ($)	Jun. 09, 2023 CAD ($)	Jun. 23, 2022 CAD ($)	Mar. 31, 2026 CAD ($)	Mar. 31, 2025 CAD ($) shares	Mar. 31, 2024 CAD ($)	Mar. 31, 2023 CAD ($)	Mar. 31, 2022 CAD ($)	Dec. 31, 2025 CAD ($)	Mar. 31, 2026 CAD ($)	Jun. 09, 2027 CAD ($)	Jan. 04, 2024 CAD ($)
Statement Line Items [Line Items]
Purchase of exploration and evaluation assets											$ 225,000	$ 249,957	$ 198,829
Increase (decrease) for purchase of evaluation and exploration assets											225,000	6,866,449
Transfer agent and filing fees											$ 296,746	$ 276,316	344,226
Foremost [member] \| Denison Mines Corp. [member]
Statement Line Items [Line Items]
Proportion of ownership interest in associate												19.95%
Major purchases of assets [member] \| Foremost [member] \| Denison Mines Corp. [member]
Statement Line Items [Line Items]
Proportion of ownership interest in associate	51.00%
Jean lake property [member]
Statement Line Items [Line Items]
Proportion of ownership interest in associate																	100.00%
Purchase of exploration and evaluation assets																	$ 250,000
Increase (decrease) for purchase of evaluation and exploration assets																	$ 250,000
Number of instruments or interests issued or issuable											47,299						47,299
Expense arising from exploration for and evaluation of mineral resources																	$ 500,000
Net Smelter Royalty Return Percentage											2.00%						2.00%
Option agreement, net smelter royalty percentage											1.00%						1.00%
Option agreement, cash payment											$ 1,000,000						$ 1,000,000
Grass river property [member]
Statement Line Items [Line Items]
Purchase of exploration and evaluation assets													1,755	$ 3,000	$ 40,500
Transfer agent and filing fees											615	$ 130	$ 1,755
Jol Lithium property [member]
Statement Line Items [Line Items]
Proportion of ownership interest in associate													100.00%
Number of instruments or interests issued or issuable														364
Net Smelter Royalty Return Percentage														2.00%
Transfer agent and filing fees												638
Cash transferred														$ 8,000
Cost of issuance of shares														$ 2,454
Peg North property [member]
Statement Line Items [Line Items]
Proportion of ownership interest in associate														100.00%
Purchase of exploration and evaluation assets							$ 100,000	$ 100,000		$ 100,000
Increase (decrease) for purchase of evaluation and exploration assets						$ 150,000	$ 100,000		$ 100,000	$ 100,000
Number of instruments or interests issued or issuable							28,818		13,072	10,526
Expense arising from exploration for and evaluation of mineral resources																$ 881,337
Net Smelter Royalty Return Percentage														2.00%
Option agreement, net smelter royalty percentage														1.00%
Option agreement, cash payment														$ 1,500,000
Peg North property [member] \| Major purchases of assets [member]
Statement Line Items [Line Items]
Purchase of exploration and evaluation assets				$ 150,000	$ 150,000	$ 150,000												$ 750,000
Increase (decrease) for purchase of evaluation and exploration assets				$ 150,000	$ 150,000													750,000
Number of instruments or interests issued or issuable					65,502	30,000
Expense arising from exploration for and evaluation of mineral resources																		$ 3,000,000
Lac Simard South property [member]
Statement Line Items [Line Items]
Proportion of ownership interest in associate													100.00%
Purchase of exploration and evaluation assets											0	0
Increase (decrease) for purchase of evaluation and exploration assets											0	$ 0
Number of instruments or interests issued or issuable													10,700
Cash transferred													$ 35,000
Equity interests of acquirer													85,600
Athabasca properties [member]
Statement Line Items [Line Items]
Proportion of ownership interest in associate												20.00%
Purchase of exploration and evaluation assets											0	$ 0
Increase (decrease) for purchase of evaluation and exploration assets											0	$ 6,716,449
Increase (decrease) in number of shares outstanding, acquisitions (in shares) \| shares												1,369,810
Increase (decrease) through acquisition of subsidiary, equity												$ 5,205,278
Athabasca properties [member] \| Finders and advisory fees [member]
Statement Line Items [Line Items]
Increase (decrease) in number of shares outstanding, acquisitions (in shares) \| shares												425,682
Increase (decrease) through acquisition of subsidiary, equity												$ 1,511,171
Athabasca properties [member] \| Top of range [member]
Statement Line Items [Line Items]
Proportion of ownership interest in associate												70.00%
Athabasca properties [member] \| Major purchases of assets [member]
Statement Line Items [Line Items]
Proportion of ownership interest in associate		19.00%	31.00%
Payments for exploration and evaluation expenses		$ 2,500,000	$ 2,000,000
Capital commitments		$ 12,000,000	$ 8,000,000								$ 7,526,205						$ 7,526,205
Hatchet Lake [member]
Statement Line Items [Line Items]
Proportion of ownership interest in associate												14.03%
Hatchet Lake [member] \| Major purchases of assets [member]
Statement Line Items [Line Items]
Proportion of ownership interest in associate		15.22%	21.75%
Manitoba Grant [Member] \| Jean Lake and Zoro Lithium properties [member]
Statement Line Items [Line Items]
Government grant agreement																			$ 300,000
Proceeds from government grants, classified as financing activities												$ 200,000	$ 100,000