| Document and Entity Information | Jul. 01, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jul. 1, 2020 |
| Entity Registrant Name | UNIFIRST CORP |
| Entity Central Index Key | 0000717954 |
| Entity Emerging Growth Company | false |
| Entity File Number | 001-08504 |
| Entity Incorporation, State or Country Code | MA |
| Entity Tax Identification Number | 04-2103460 |
| Entity Address, Address Line One | 68 Jonspin Road |
| Entity Address, City or Town | Wilmington |
| Entity Address, State or Province | MA |
| Entity Address Postal Zip Code | 01887 |
| City Area Code | 978 |
| Local Phone Number | 658-8888 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of each class | Common Stock, $0.10 par value per share |
| Trading symbol | UNF |
| Name of each exchange on which registered | NYSE |
