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Employee Benefit Plans - Narrative (Details) - USD ($) $ in Millions | 12 Months Ended
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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 |

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- Definition The minimum annual interest rate which is applied to the plan amount invested in a Guaranteed Deposit Account. + References No definition available. + Details
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- Definition Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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- Definition Amount of cost (reversal of cost) for pension benefits. Excludes other postretirement benefits. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(b)(2)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(b)(4)) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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