Employee Benefit Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 25, 2018	Aug. 26, 2017	Aug. 27, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions charged to expense under the plan	$ 18.1	$ 15.0	$ 13.8
UniFirst Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount charged to expense related to the plan	$ 0.3	0.5	0.4
Minimum annual interest rate	3.25%
Textilease Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount charged to expense related to the plan	$ 0.2	0.2	0.2
Minimum annual interest rate	1.50%
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated benefit obligations	$ 7.4	8.3
SERP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount charged to expense related to the plan	2.1	2.5	$ 2.4
Accumulated benefit obligations	$ 21.7	$ 22.3