Available increase in aggregate amount borrowed

No definition available.

Name:	msm_AvailableIncreaseInAggregateAmountBorrowed
Namespace Prefix:	msm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fronting fee is the administrative fee paid to the lead credit issuer.

+ References

No definition available.

+ Details

Name:	msm_QuarterlyFrontingFee
Namespace Prefix:	msm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Repayment of debt using cash on hand.

+ References

No definition available.

+ Details

Name:	msm_RepaymentOfDebtUsingCashOnHand
Namespace Prefix:	msm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Usage fee, percent

+ References

No definition available.

+ Details

Name:	msm_UsageFeePercent
Namespace Prefix:	msm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentMaturityDate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The effective interest rate at the end of the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

Name:	us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of cash inflow from contractual arrangement with the lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

Name:	us-gaap_ProceedsFromLinesOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of cash outflow for payment of an obligation from a lender, including but not limited to, letter of credit, standby letter of credit and revolving credit arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

Name:	us-gaap_RepaymentsOfLinesOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash outflow for a borrowing having initial term of repayment within one year or the normal operating cycle, if longer.

+ References

+ Details

Name:	us-gaap_RepaymentsOfShortTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=msm_PreviousCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=msm_TermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=msm_NewCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=msm_FederalFundsEffectiveRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=msm_LeverageRatioMarginMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt And Capital Lease Obligations (Credit Facility) (Narrative) (Details) - USD ($)	12 Months Ended
	Sep. 02, 2017	Sep. 03, 2016	Aug. 29, 2015	Mar. 31, 2017
Debt Instrument [Line Items]
Borrowings under Credit Facility	$ 546,000,000	$ 305,000,000	$ 336,000,000
Repayments of debt	618,500,000	301,000,000	$ 243,000,000
New Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity	$ 600,000,000
Maturity date	Apr. 14, 2022
Credit facility, expiration term	5 years
Available increase in amount borrowed	$ 300,000,000
Payments under revolving loans from credit facility	236,000,000	276,000,000
Borrowings under Credit Facility	330,000,000
Previous Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity				$ 650,000,000
Payments under revolving loans from credit facility	345,000,000
Repayment of debt using cash on hand	16,706,000
Borrowings under Credit Facility	216,000,000
Term Loan [Member]
Debt Instrument [Line Items]
Repayments of debt	37,500,000	$ 25,000,000
Letter of Credit [Member]
Debt Instrument [Line Items]
Credit facility, maximum borrowing capacity	$ 50,000,000
Quarterly fronting fee	0.125%
New Credit Facility [Member]
Debt Instrument [Line Items]
Borrowing rate under Credit Facility	2.36%
LIBOR [Member] \| New Credit Facility [Member]
Debt Instrument [Line Items]
Percentage points in addition to reference rate used in computation of variable rate on debt instrument	1.125%
Federal Funds Effective Rate [Member] \| New Credit Facility [Member]
Debt Instrument [Line Items]
Percentage points in addition to reference rate used in computation of variable rate on debt instrument	0.50%
Minimum [Member] \| New Credit Facility [Member]
Debt Instrument [Line Items]
Quarterly undrawn fee	0.10%
Minimum [Member] \| LIBOR [Member] \| New Credit Facility [Member]
Debt Instrument [Line Items]
Percentage points in addition to reference rate used in computation of variable rate on debt instrument	1.00%
Minimum [Member] \| Leverage Ratio Margin [Member] \| New Credit Facility [Member]
Debt Instrument [Line Items]
Percentage points in addition to reference rate used in computation of variable rate on debt instrument	0.00%
Minimum [Member] \| Leverage Ratio Margin [Member] \| Letter of Credit [Member]
Debt Instrument [Line Items]
Usage fee, percent	1.00%
Maximum [Member] \| New Credit Facility [Member]
Debt Instrument [Line Items]
Quarterly undrawn fee	0.20%
Maximum [Member] \| LIBOR [Member] \| New Credit Facility [Member]
Debt Instrument [Line Items]
Percentage points in addition to reference rate used in computation of variable rate on debt instrument	1.375%
Maximum [Member] \| Leverage Ratio Margin [Member] \| New Credit Facility [Member]
Debt Instrument [Line Items]
Percentage points in addition to reference rate used in computation of variable rate on debt instrument	0.375%
Maximum [Member] \| Leverage Ratio Margin [Member] \| Letter of Credit [Member]
Debt Instrument [Line Items]
Usage fee, percent	1.375%