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v3.25.2

COMMON SHARES (Details 3) - November Private Warrantsliabilities [Member] $ in Thousands | 8 Months Ended
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Jun. 30, 2025 USD ($)
Subsidiary, Sale of Stock [Line Items] |
Beginning balance | $ 1,929
Fair value of Warrants exercised | (338)
Change in fair value | 2,240
Ending balance | $ 3,831

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- Definition The element represents changes in fair value of initial valuation1. + References No definition available. + Details
Name: | niobf_ChangesInFairValueOfInitialValuation1
Namespace Prefix: | niobf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The element represents fair value of warrants exercised. + References No definition available. + Details
Name: | niobf_FairValueOfWarrantsExercised
Namespace Prefix: | niobf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition The element represents servicing assets at fair value changes in fair value resulting from changes in valuation inputs. + References No definition available. + Details
Name: | niobf_ServicingAssetsAtFairValueChangesInFairValueResultingFromChangesInValuationInputs
Namespace Prefix: | niobf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_SubsidiarySaleOfStockLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_SubsidiarySaleOfStockAxis=niobf_NovemberPrivateWarrantsliabilitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |