Represents the deposit amount in business acquisition.

No definition available.

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Namespace Prefix:	npk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

In a business combination in which the amount of net identifiable assets acquired and liabilities assumed exceeds the aggregate consideration transferred or to be transferred (as defined), this element represents the amount of gain recognized by the entity.

+ References

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+ Details

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

- Definition

This element represents the amount of earnings or loss of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

+ References

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-Publisher FASB
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period.

+ References

+ Details

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

- Definition

Amount of currency on hand as well as demand deposits with banks or financial institutions, acquired at the acquisition date. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

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

- Definition

The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

+ References

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- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

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Namespace Prefix:
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Period Type:

Note P - Business Acquisition (Details Textual) - USD ($)			5 Months Ended	12 Months Ended
	Oct. 26, 2022	Jul. 29, 2022	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Business Combination, Bargain Purchase, Gain Recognized, Amount				$ 492,000	$ (0)	$ (0)
Knox Safety, Inc [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents		$ 3,125,000
Deposits, Business Acquisition		500,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual			$ 265,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual			$ (1,546,000)
Knox Safety, Inc [Member] \| Selling, General and Administrative Expenses [Member]
Business Combination, Bargain Purchase, Gain Recognized, Amount		$ 492,000
Knox Safety, Inc [Member] \| Trademarks and Safety Certifications [Member]
Acquired Finite-Lived Intangible Assets, Weighted Average Useful Life (Year)		2 years
Woodlawn Manufacturing, Ltd [Member]
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	$ 3,219,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual	101,000
Payments to Acquire Businesses, Gross	$ 21,558,000
Woodlawn Manufacturing, Ltd [Member] \| Trademarks and Safety Certifications [Member]
Acquired Finite-Lived Intangible Assets, Weighted Average Useful Life (Year)	4 years