Document And Entity Information - shares	9 Months Ended
	May 27, 2017	Jun. 30, 2017
Document Information [Line Items]
Entity Registrant Name	Unifirst Corp
Entity Central Index Key	0000717954
Trading Symbol	unf
Current Fiscal Year End Date	--08-26
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	May 27, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Amendment Flag	false
Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		15,421,381
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		4,845,519