Document And Entity Information - shares	6 Months Ended
	Feb. 25, 2017	Mar. 31, 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
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	Yes
Document Type	10-Q
Document Period End Date	Feb. 25, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q2
Amendment Flag	false
Common Class B [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding (in shares)		4,845,519
Common Class A [Member]
Document Information [Line Items]
Entity Common Stock, Shares Outstanding (in shares)		15,462,689