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Note G - Other Assets (Details Textual) - USD ($)	Sep. 28, 2025	Dec. 31, 2024
Housewares/Small Appliances [Member]
Materials, Supplies, and Other	$ 2,072,000	$ 2,929,000

X

- Definition

The carrying amount of capitalized costs of materials, supplies, and other assets, which are not included in inventory but used in production.

+ References

No definition available.

+ Details

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

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=npk_HousewaresSmallAppliancesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: