Asset Retirement Obligations - Narrative (Details)	6 Months Ended
Feb. 29, 2020
Minimum
Asset Retirement Obligations [Line Items]
Remaining lives	1 year
Maximum
Asset Retirement Obligations [Line Items]
Remaining lives	24 years

This element describes the minimum years the Company will discount the liability of estimated future costs to decommission one of its facilities.

No definition available.

Name:	unf_AssetRetirementObligationRemainingLives
Namespace Prefix:	unf_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration