Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Mar. 01, 2020	Jun. 30, 2019
Document And Entity Information [Abstract]
Document Type	10-K
Current Fiscal Year End Date	--12-31
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Entity File Number	1-2451
Entity Registrant Name	NATIONAL PRESTO INDUSTRIES INC
Entity Incorporation, State Country Name	WI
Entity Tax Identification Number	390494170
Entity Address, Address Line One	3925 North Hastings Way
Entity Address, City or Town	Eau Claire
Entity Address, State or Province	WI
Entity Address, Postal Zip Code	54703-3703
City Area Code	715
Local Phone Number	839-2121
Trading Symbol	NPK
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 462,078,337
Entity Common Stock, Shares Outstanding		7,006,323
Entity Central Index Key	0000080172
Document Fiscal Period Focus	FY
Amendment Flag	false