Document And Entity Information - shares	9 Months Ended
	May 26, 2018	Jun. 29, 2018
Document Information [Line Items]
Entity Registrant Name	Unifirst Corporation
Entity Central Index Key	0000717954
Trading Symbol	unf
Current Fiscal Year End Date	--08-25
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	May 26, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		15,427,583
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,711,009