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v3.19.3

Fair Value (Details) - USD ($) | 12 Months Ended |  |
--- | --- | --- | ---
Aug. 31, 2019 | Sep. 01, 2018 | Aug. 31, 2013
Fair Value [Abstract] |  |  |
Cash equivalents, fair value | $ 0 | $ 0 |
Taxable bonds |  | $ 27,025,000 | $ 27,025,000
Gains and losses on securities | 0 |  |
Fair value remeasurement of non-financial assets on non-recurring basis | 0 |  |
Fair value remeasurement of non-financial liabilities on non-recurring basis | $ 0 |  |

X
- Definition Cash Equivalents Fair Value Disclosure + References No definition available. + Details
Name: | msm_CashEquivalentsFairValueDisclosure
Namespace Prefix: | msm_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of addition (reduction) to the amount at which an asset could be incurred (settled) in a current transaction between willing parties. + References No definition available. + Details
Name: | us-gaap_AssetsFairValueAdjustment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References No definition available. + Details
Name: | us-gaap_AvailableforsaleSecuritiesGrossRealizedGainLossExcludingOtherThanTemporaryImpairments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_FairValueDisclosuresAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of addition (reduction) to the amount at which a liability could be incurred (settled) in a current transaction between willing parties. + References No definition available. + Details
Name: | us-gaap_LiabilitiesFairValueAdjustment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration