Note M - Subsequent Event (Details Textual) - Subsequent Event [Member] - USD ($)	Jul. 31, 2025	Jul. 29, 2025
AMTEC Corporation [Member]
Government Assistance, Award Amount		$ 101,100,000
OneEvent Technologies, Inc. [Member] \| Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations [Member]
Proceeds from Sale of Productive Assets	$ 279,000
Sale of Assets of Subsidiary, Contingent Consideration, Amount	$ 275,000

Represents the amount of contingent consideration included in the sale of assets of a subsidiary.

No definition available.

Name:	npk_SaleOfAssetsOfSubsidiaryContingentConsiderationAmount
Namespace Prefix:	npk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of government assistance awarded that comprises amount received, receivable, and to be received unless condition for government assistance is not met. Includes, but is not limited to, government grant, assistance, incentive, award, subsidy, and loan.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 832
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483507/832-10-50-3

+ Details

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

- Definition

The cash inflow from the sale of property, plant and equipment (capital expenditures), software, and other intangible assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 12
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-12

+ Details

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

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=npk_AMTECCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidatedEntitiesAxis=npk_OneEventTechnologiesIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DisposalGroupDisposedOfByMeansOtherThanSaleNotDiscontinuedOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: