Document and Entity Information - shares	6 Months Ended
	Feb. 23, 2019	Mar. 29, 2019
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Feb. 23, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
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 Emerging Growth Company	false
Entity Small Business	false
Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		15,352,793
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,710,009