| Document And Entity Information (USD $)
|
12 Months Ended | ||
|---|---|---|---|
| Dec. 31, 2011
|
Mar. 02, 2012
|
Jun. 30, 2011
|
|
| Document And Entity Information [Abstract] | |||
| Document Type | 10-K | ||
| Amendment Flag | false | ||
| Document Period End Date | Dec. 31, 2011 | ||
| Document Fiscal Period Focus | FY | ||
| Document Fiscal Year Focus | 2011 | ||
| 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 | 6,875,001 | ||
| Entity Well-known Seasoned Issuer | No | ||
| Entity Public Float | $ 490,468,015 | ||
| Entity Current Reporting Status | Yes | ||
| Entity Voluntary Filers | No |