Description of the ownership interests which are represented by units.

No definition available.

Name:	niobf_DescriptionOfUnits
Namespace Prefix:	niobf_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Period the instrument, asset or liability is expected to be outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueAssumptionsExpectedTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Measure of dispersion, in percentage terms (for instance, the standard deviation or variance), for a given stock price.

+ References

+ Details

Name:	us-gaap_FairValueAssumptionsExpectedVolatilityRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Risk-free interest rate assumption used in valuing an instrument.

+ References

+ Details

Name:	us-gaap_FairValueAssumptionsRiskFreeInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of cash paid for commissions during the current period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3536-108585

+ Details

Name:	us-gaap_PaymentsForCommissions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Cash received on stock transaction after deduction of issuance costs.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockConsiderationReceivedOnTransaction
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The number of shares issued or sold by the subsidiary or equity method investee per stock transaction.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockPricePerShare
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementEquityComponentsAxis=niobf_Warrant2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CurrencyAxis=currency_CAD
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsidiarySaleOfStockAxis=us-gaap_PrivatePlacementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=niobf_ShareBasedCompensationAwardTrancheTwo1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=niobf_ShareBasedCompensationAwardTrancheTwo2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

COMMON STOCK (Details Narrative) CAD / shares in Units, CAD in Thousands, $ in Thousands			1 Months Ended	12 Months Ended
	Feb. 14, 2017 CAD CAD / shares shares	Jan. 19, 2016 USD ($) shares	Feb. 28, 2017 CAD CAD / shares shares	Jun. 30, 2017	Jun. 30, 2016	Jan. 19, 2016 CAD / shares
Risk free interest rate				1.25%	1.25%
Volatility				51.14%	88.63%
Expected life				1 year 3 months	2 years 3 months
Broker Warrant [Member]
Plan award term			3 years
Number of units issued			78,342
Risk free interest rate			0.75%
Volatility			81.27%
Expected life			3 years
CAD \| Broker Warrant [Member]
Unit price (in dollars per unit) \| CAD / shares			CAD 26
Non-Brokered Private Placement [Member]
Number of units issued		9,074,835
Gross proceeds from units issued \| $		$ 3,750
Non-Brokered Private Placement [Member] \| Broker Warrant [Member]
Risk free interest rate		0.75%
Volatility		100.13%
Expected life		3 years
Non-Brokered Private Placement [Member] \| CAD
Unit price (in dollars per unit) \| CAD / shares						CAD 0.57
Non-Brokered Private Placement [Member] \| Tranche One [Member]
Number of units issued	3,860,800
Description of units	Each Unit consists of one Common Share and one transferable Common Share purchase warrant (each whole such warrant a "Warrant"), with each Warrant entitling the holder thereof to acquire one additional Common Share at a price of C$0.85 for a period of 36 months from their date of issuance.
Non-Brokered Private Placement [Member] \| Tranche One [Member] \| CAD
Unit price (in dollars per unit) \| CAD / shares	CAD 0.70
Gross proceeds from units issued \| CAD	CAD 2,700
Non-Brokered Private Placement [Member] \| Tranche Two [Member]
Number of units issued			3,503,989
Description of units			Each Final Closing Unit consists of one Common Share and one transferable Common Share purchase warrant (a "Warrant"), with each Warrant entitling the holder thereof to acquire one additional Common Share at a price of C$0.85 for a period of three years from Unit issuance.
Non-Brokered Private Placement [Member] \| Tranche Two [Member] \| CAD
Unit price (in dollars per unit) \| CAD / shares			CAD 0.70
Gross proceeds from units issued \| CAD			CAD 2,500
Cash commissions paid \| CAD			CAD 88
Non-Brokered Private Placement [Member] \| Tranche Two, Dated on February 21, 2017 [Member]
Number of units issued			2,964,682
Non-Brokered Private Placement [Member] \| Tranche Two, Dated on February 28, 2017 [Member]
Number of units issued			539,307