Revenue Recognition - Narrative (Details) $ in Millions	3 Months Ended	6 Months Ended
Feb. 23, 2019 USD ($)	Feb. 23, 2019 USD ($)
Disaggregation of Revenue [Line Items]
Percentage of revenues derived from route servicing fees		91.00%
Amortization expense related to deferred commissions	$ 2.9	$ 5.7
Current assets related to deferred commissions	10.8	10.8
Noncurrent assets related to deferred commissions	$ 44.6	$ 44.6
Core Laundry Operations
Disaggregation of Revenue [Line Items]
Percentage of revenues recognized over time	95.30%	95.30%
Percentage of revenues recognized at a point in time	4.70%	4.70%
Specialty Garments
Disaggregation of Revenue [Line Items]
Percentage of revenues recognized over time	82.20%	83.10%
Percentage of revenues recognized at a point in time	17.80%	16.90%
First Aid
Disaggregation of Revenue [Line Items]
Percentage of revenues recognized at a point in time	100.00%	100.00%

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

No definition available.

Name:	unf_RevenueFromContractsWithCustomersPercentageOfRevenuesFromRouteServicingFees
Namespace Prefix:	unf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenue, Performance Obligation, Percentage Of Revenues Satisfied At A Point In Time

+ References

No definition available.

+ Details

Name:	unf_RevenuePerformanceObligationPercentageOfRevenuesSatisfiedAtAPointInTime
Namespace Prefix:	unf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Revenue, Performance Obligation, Percentage Of Revenues Satisfied Over Time

+ References

No definition available.

+ Details

Name:	unf_RevenuePerformanceObligationPercentageOfRevenuesSatisfiedOverTime
Namespace Prefix:	unf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of amortization expense for asset recognized from cost incurred to obtain or fulfill contract with customer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=68051541&loc=SL49131252-203054

+ Details

Name:	us-gaap_CapitalizedContractCostAmortization
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/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 340
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=68051541&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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=unf_USandCanadianRentalandCleaningMFGandCorporateSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=unf_SpecialtyGarmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=unf_FirstAidMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: