Document And Entity Information - shares	3 Months Ended
	Nov. 25, 2017	Dec. 29, 2017
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
Document Type	10-Q
Document Period End Date	Nov. 25, 2017
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Amendment Flag	false
Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		15,474,582
Class B Common Stock
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		4,815,519