Revenue Recognition - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Feb. 25, 2023	Feb. 26, 2022	Feb. 25, 2023	Feb. 26, 2022	Aug. 27, 2022
Revenue from Contract with Customer [Abstract]
Percentage of revenues derived from route servicing fees	88.40%	91.50%	88.30%	91.40%
Current assets related to deferred commissions	$ 15.9		$ 15.9		$ 15.2
Noncurrent assets related to deferred commissions	68.0		68.0		$ 65.1
Amortization expense related to deferred commissions	$ 4.1	$ 3.8	$ 8.1	$ 7.6

Revenue From Contracts With Customers, Percentage Of Revenues From Route Servicing Fees

No definition available.

Name:	unf_RevenueFromContractsWithCustomersPercentageOfRevenuesFromRouteServicingFees
Namespace Prefix:	unf_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of expense recognized in the current period for the periodic realization of capitalized fees that were paid to salespeople, distributors, brokers, and agents at the time of the conclusion of the sale. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.3)
-URI https://asc.fasb.org/extlink&oid=126953954&loc=SL114868664-224227

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3602-108585

+ Details

Name:	us-gaap_AmortizationOfDeferredSalesCommissions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount, after accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer; classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126905575&loc=SL49131252-203054

+ Details

Name:	us-gaap_CapitalizedContractCostNetCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, after accumulated amortization and accumulated impairment loss, of asset recognized from cost incurred to obtain or fulfill contract with customer; classified as noncurrent.

+ References

+ Details

Name:	us-gaap_CapitalizedContractCostNetNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_RevenueFromContractWithCustomerAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration