Employee Benefit Plans - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Aug. 26, 2017	Aug. 27, 2016	Aug. 29, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contributions charged to expense under the plan	$ 15.0	$ 13.8	$ 15.8
Amount charged to expense related to the plan	2.5	2.4	2.8
UniFirst Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Amount charged to expense related to the plan	$ 0.5	0.4	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	$ 0.3
Minimum annual interest rate	1.50%
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated benefit obligations	$ 8.3	8.9
SERP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated benefit obligations	$ 22.3	$ 30.7