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Balance Type:	na
Period Type:	duration

Amount of expense on certain equity based compensation arrangements, such as stock appreciation rights, deferred compensation agreements and liabilities to noncontrolling interest holders.

No definition available.

Name:	gms_TotalExpenseStockAppreciationRightsDeferredCompensationAndRedeemableNoncontrollingInterestsArrangements
Namespace Prefix:	gms_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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Aggregate carrying value as of the balance sheet date of the liabilities for stock option plans and other equity-based compensation arrangements payable within one year (or the operating cycle, if longer).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Aggregate carrying value as of the balance sheet date of the liabilities for stock option plans and other equity-based compensation arrangements payable after one year (or the operating cycle, if longer).

No definition available.

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Data Type:	xbrli:monetaryItemType
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Aggregate carrying value as of the balance sheet date of the liabilities for stock option plans and other equity-based compensation arrangements.

No definition available.

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of addition (reduction) to the amount at which a liability could be incurred (settled) in a current transaction between willing parties.

No definition available.

Name:	us-gaap_LiabilitiesFairValueAdjustment
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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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.

No definition available.

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
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Data Type:	xbrli:stringItemType
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Period Type:	duration

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Namespace Prefix:
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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_AwardTypeAxis=gms_ShareholderDeferredCompensationMember
Namespace Prefix:
Data Type:	na
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Period Type: