| Document And Entity Information | Aug. 18, 2020 |
| Document Information [Line Items] | |
| Entity, Registrant Name | Insteel Industries, Inc. |
| Document, Type | 8-K |
| Document, Period End Date | Aug. 18, 2020 |
| Entity, File Number | 1-9929 |
| Entity, Incorporation, State or Country Code | NC |
| Entity, Tax Identification Number | 56-0674867 |
| Entity, Address, Address Line One | 1373 Boggs Drive |
| Entity, Address, City or Town | Mount Airy |
| Entity, Address, State or Province | NC |
| Entity, Address, Postal Zip Code | 27030 |
| City Area Code | 336 |
| Local Phone Number | 786-2141 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | IIIN |
| Security Exchange Name | NASDAQ |
| Entity, Emerging Growth Company | false |
| Amendment Flag | false |
| Entity, Central Index Key | 0000764401 |
