Acquisitions - Narrative (Details) $ in Millions	6 Months Ended
Feb. 29, 2020 USD ($) Business
Business Acquisition [Line Items]
Number of business acquired \| Business	8
Business acquisitions, aggregate purchase price	$ 41.3
Missouri Acquisition
Business Acquisition [Line Items]
Business acquisitions, aggregate purchase price	38.8
Business combination, provisional information, initial accounting incomplete, adjustment, tangible assets	4.4
Business combination, provisional information, initial accounting incomplete, adjustment, goodwill	23.5
Business combination, provisional information, initial accounting incomplete, adjustment, intangibles	$ 10.9

Business combination, provisional information, initial accounting incomplete, adjustment, goodwill.

No definition available.

Name:	unf_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentGoodwill
Namespace Prefix:	unf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Business combination, provisional information, initial accounting incomplete, adjustment, tangible assets.

+ References

No definition available.

+ Details

Name:	unf_BusinessCombinationProvisionalInformationInitialAccountingIncompleteAdjustmentTangibleAssets
Namespace Prefix:	unf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Definition

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6613-128477

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 30
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=116859721&loc=d3e6578-128477

+ Details

Name:	us-gaap_BusinessCombinationConsiderationTransferred1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This element represents the amount of any measurement period adjustment (as defined) realized during the reporting period to intangibles acquired in connection with a business combination for which the initial accounting was incomplete.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 20
-Section 50
-Paragraph 4A
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=116869197&loc=SL65897772-128472

+ Details

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

- Definition

The number of businesses acquired by the entity during the period.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfBusinessesAcquired
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_BusinessAcquisitionAxis=unf_MissouriAcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: