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The changes in the April 2024 Notes and the April 2024 Warrant liability are presented below, respectively (Details) $ in Thousands	9 Months Ended
	Mar. 31, 2025 USD ($)
Debt Disclosure [Abstract]
Fair value at June 30, 2024	$ 7,089
Principal payments	(7,129)
Change in fair value	40
Fair value at December 31, 2024

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- Definition

The element represents change in fair value.

+ References

No definition available.

+ Details

Name:	niobf_ChangeInFairValue
Namespace Prefix:	niobf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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- References

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of the required periodic payments including both interest and principal payments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-SubTopic 10
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477734/942-470-50-3

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
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- Definition

Fair value of all derivative assets designated as fair value hedging instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4B

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	instant