Represents the floor of the variable rate on the debt instrument.

No definition available.

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Period Type:	duration

- Definition

Write-off of amounts previously capitalized as debt issuance cost and unamortized debt discount (net of debt premium) that was originally recognized at the issuance of the instrument in an extinguishment of debt.

+ References

No definition available.

+ Details

Name:	gms_WriteOffOfDeferredDebtIssuanceCostAndUnamortizedDiscountPremiumNet
Namespace Prefix:	gms_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

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

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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

- 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

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The interest rate applicable to the portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

+ 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)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The cash outflow to repay long-term debt that is wholly or partially secured by collateral. Excludes repayments of tax exempt secured debt.

+ 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

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=gms_FirstLienTermLoanDue2025Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gms_SecondAmendmentToFirstLienCreditAgreementDated07June2017Member
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_DebtInstrumentAxis=gms_ThirdAmendmentToFirstLienCreditAgreementDated01June2018Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=gms_AssetBasedLendingCreditFacilityDatedAsOf2014April01Member
Namespace Prefix:
Data Type:	na
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Period Type:

Long-Term Debt - Acquisition Debt (Details) - USD ($) $ in Thousands			6 Months Ended
	Jun. 01, 2018	Jun. 07, 2017	Oct. 31, 2018	Oct. 31, 2017
Long-term debt
Loan repayment			$ 571,840	$ 477,616
Write-off of debt discount and deferred financing fees				74
First Lien Term Loan Due 2025
Long-term debt
Loan repayment	$ 571,800	$ 477,600
Second amendment to First Lien Credit Agreement
Long-term debt
Aggregate principal amount		$ 577,600
Write-off of debt discount and deferred financing fees				$ 100
Second amendment to First Lien Credit Agreement \| LIBOR
Long-term debt
Margin added to variable rate (as a percent)		3.00%
Variable rate floor (as a percent)		1.00%
Third Amendment
Long-term debt
Aggregate principal amount	$ 996,800
Borrowing interest rate (as a percent)	5.05%
Third Amendment \| LIBOR
Long-term debt
Margin added to variable rate (as a percent)	2.75%
Variable rate floor (as a percent)	0.00%
ABL Facility
Long-term debt
Loan repayment			$ 94,000
Borrowing interest rate (as a percent)			3.93%