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Note 5 - Investment in Galore Creek (Details Textual) - Galore Creek [Member]	Feb. 28, 2018
Equity Method Investment, Ownership Percentage	50.00%
Unconsolidated Ventures, Number of Directors	4
Unconsolidated Ventures, Number of Directors, Selected By the Reporting Entity	2
Teck [Member]
Equity Method Investment, Ownership Percentage	50.00%
Unconsolidated Ventures, Number of Directors Selected By Venture Partners	2

X

- Definition

Represents the total number of directors on the board of an unconsolidated venture, including those selected by the reporting entity and/or the venture partner.

+ References

No definition available.

+ Details

Name:	ng_UnconsolidatedVenturesNumberOfDirectors
Namespace Prefix:	ng_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Represents the number of directors on the board of unconsolidated ventures, which directors are selected by the reporting entity.

+ References

No definition available.

+ Details

Name:	ng_UnconsolidatedVenturesNumberOfDirectorsSelectedByTheReportingEntity
Namespace Prefix:	ng_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

Represents the number of directors on the board of unconsolidated ventures, which directors are selected by the reporting entity's venture partners.

+ References

No definition available.

+ Details

Name:	ng_UnconsolidatedVenturesNumberOfDirectorsSelectedByVenturePartners
Namespace Prefix:	ng_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

X

- Details

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

X

- Details

Name:	dei_LegalEntityAxis=ng_TeckMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: