Document and Entity Information - USD ($)	12 Months Ended
	Aug. 31, 2019	Oct. 25, 2019	Feb. 22, 2019
Document Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Aug. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Registrant Name	UNIFIRST CORP
Entity Central Index Key	0000717954
Current Fiscal Year End Date	--08-31
Entity Filer Category	Large Accelerated Filer
Trading Symbol	UNF
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity File Number	001-08504
Entity Tax Identification Number	042103460
Entity Address, Address Line One	68 Jonspin Road
Entity Address, City or Town	Wilmington
Entity Address, State or Province	Massachusetts
Entity Address, Postal Zip Code	01887
City Area Code	(978)
Local Phone Number	658-8888
Entity Address, Country	UNITED STATES
Entity Public Float			$ 2,229,068,691
Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		15,294,444
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,643,009