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Note 12 - Share-based Compensation - PSU Awards Outstanding and PSU Activity (Details) - Performance Share Units [Member] $ / shares in Units, $ in Thousands	3 Months Ended
	Feb. 28, 2025 USD ($) $ / shares shares
Balance, Numbers of awards (in shares) | shares	1,633,500
Balance, weighted average grant day fair value per award (in dollars per share) | $ / shares	$ 5.32
Vested, Numbers of awards (in shares) | shares	(102,100)
Vested, weighted average grant day fair value per award (in dollars per share) | $ / shares	$ 6.67
Performance adjustment, Numbers of awards (in shares) | shares	(306,300)
Performance adjustment, weighted average grant day fair value per award (in dollars per share) | $ / shares	$ 6.67
Balance, Numbers of awards (in shares) | shares	1,225,100
Balance, weighted average grant day fair value per award (in dollars per share) | $ / shares	$ 4.87
Balance, intrinsic value | $	$ 0

X

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were adjusted based on performance during the reporting period.

+ References

No definition available.

+ Details

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Namespace Prefix:	ng_
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Balance Type:	na
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X

- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were adjusted based on performance.

+ References

No definition available.

+ Details

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Namespace Prefix:	ng_
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Period Type:	duration

X

- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(ii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

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X

- Definition

Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(ii)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

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Balance Type:	na
Period Type:	instant

X

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(02)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

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Balance Type:	na
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X

- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 718
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(02)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480429/718-10-50-2

+ Details

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Balance Type:	na
Period Type:	duration

X

- Definition

Intrinsic value of nonvested award under share-based payment arrangement. Excludes share and unit options.

+ References

No definition available.

+ Details

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