The amount of accumulated accretion associated with the financing receivable.

No definition available.

Name:	ng_FinancingReceivableAccumulatedAccretion
Namespace Prefix:	ng_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Value of input used to measure notes receivable.

+ References

No definition available.

+ Details

Name:	ng_NotesReceivableMeasurementInput
Namespace Prefix:	ng_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value portion of an agreement for an unconditional promise by the maker to pay the holder a definite sum of money at a future date.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI https://asc.fasb.org/extlink&oid=123594938&loc=d3e13433-108611

+ Details

Name:	us-gaap_NotesReceivableFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost, after allowance for credit loss, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919230-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=124259787&loc=d3e4428-111522

+ Details

Name:	us-gaap_NotesReceivableNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The cash inflow associated with principal collections from a borrowing supported by a written promise to pay an obligation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3179-108585

+ Details

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

- Definition

The cash inflow associated with the deconsolidation of a previously consolidated subsidiary or sale of an entity that is related to it but not strictly controlled.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3179-108585

+ Details

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

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=ng_NoteReceivableUponCompletionOfGaloreCreekProjectPrefeasibilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=ng_NoteReceivableUponCompletionOfGaloreCreekProjectFeasibilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputExpectedTermMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDiscountRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=ng_NoteReceivableUponApprovalOfGaloreCreekProjectConstructionPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis=ng_GaloreCreekMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 4 - Notes Receivable (Details Textual) $ in Thousands			3 Months Ended		9 Months Ended
Note 4 - Notes Receivable (Details Textual) $ in Thousands	Jul. 27, 2021 USD ($)	Jul. 27, 2018 USD ($)	Aug. 31, 2022 USD ($) yr	Aug. 31, 2021 USD ($)	Aug. 31, 2022 USD ($) yr	Aug. 31, 2021 USD ($)	May 31, 2022 USD ($)	Feb. 28, 2022
Proceeds from Collection of Notes Receivable			$ 0	$ 75,000	$ 0	$ 75,000
Note Receivable Upon Completion of Galore Creek Project Pre-feasibility [Member]
Financing Receivable, after Allowance for Credit Loss, Total		$ 75,000	75,000		75,000
Proceeds from Collection of Notes Receivable	$ 75,000
Note Receivable Upon Completion of Galore Creek Project Feasibility [Member]
Financing Receivable, after Allowance for Credit Loss, Total		25,000	25,000		25,000		$ 25,000
Notes Receivable, Fair Value Disclosure			24,204		24,204
Financing Receivable, Accumulated Accretion			$ 3,256		$ 3,256
Note Receivable Upon Completion of Galore Creek Project Feasibility [Member] \| Measurement Input, Expected Term [Member]
Notes Receivable, Measurement Input (Year) \| yr			5		5
Note Receivable Upon Completion of Galore Creek Project Feasibility [Member] \| Measurement Input, Discount Rate [Member]
Notes Receivable, Measurement Input (Year)								0.036
Note Receivable Upon Approval of Galore Creek Project Construction Plan [Member]
Financing Receivable, after Allowance for Credit Loss, Total		75,000
Notes Receivable, Fair Value Disclosure		0
Galore Creek [Member]
Proceeds from Divestiture of Interest in Subsidiaries and Affiliates, Total		$ 100,000