Document And Entity Information - USD ($)	12 Months Ended
	Aug. 25, 2018	Oct. 12, 2018	Feb. 23, 2018
Document Information [Line Items]
Entity Registrant Name	Unifirst Corp
Entity Central Index Key	0000717954
Trading Symbol	unf
Current Fiscal Year End Date	--08-25
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Entity Public Float			$ 2,422,512,285
Document Type	10-K
Document Period End Date	Aug. 25, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Amendment Flag	false
Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		15,431,209
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,710,009