Document And Entity Information (USD $)
12 Months Ended
Dec. 31, 2012
Mar. 01, 2013
Jul. 01, 2012
Document And Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2012    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2012    
Entity Registrant Name NATIONAL PRESTO INDUSTRIES INC    
Entity Central Index Key 0000080172    
Current Fiscal Year End Date --12-31    
Entity Filer Category Accelerated Filer    
Entity Common Stock, Shares Outstanding   6,894,158  
Entity Current Reporting Status Yes    
Entity Public Float     $ 335,654,958
Entity Voluntary Filers No    
Entity Well-known Seasoned Issuer No