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v3.23.3

Changes in the valuation allowance are as follows: (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Jun. 30, 2023 | Jun. 30, 2022
Income Tax Disclosure [Abstract] |  |
Valuation allowance, beginning of year | $ (18,948) | $ (17,235)
Current year additions | (4,341) | (1,713)
Startup and organizational costs acquired | (2,174) |
Valuation allowance, end of year | $ (25,463) | $ (18,948)

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- Definition The element represents deferred tax assets valuation allowance additions. + References No definition available. + Details
Name: | niobf_DeferredTaxAssetsValuationAllowanceAdditions
Namespace Prefix: | niobf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Development costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 932 -SubTopic 235 -Section 50 -Paragraph 18 -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=126939881&loc=d3e62014-109447 + Details
Name: | us-gaap_CostsIncurredDevelopmentCosts
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=121826272&loc=d3e32537-109319 + Details
Name: | us-gaap_DeferredTaxAssetsValuationAllowance
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_IncomeTaxDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration