The number of geographic divisions in which the entity operates.

No definition available.

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Namespace Prefix:	gms_
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Balance Type:	na
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- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=64834752&loc=SL49117168-202975

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

+ Details

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

- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

+ References

No definition available.

+ Details

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

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

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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

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- Details

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- Details

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- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=gms_MidwestRegionOperatingSegmentMember
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- Details

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Segments - Number (Details) $ in Thousands	12 Months Ended
Segments - Number (Details) $ in Thousands	Apr. 30, 2017 USD ($) segment division	Apr. 30, 2015 USD ($) segment	May 01, 2016 USD ($)	Apr. 30, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments \| segment	7	6
Number of geographic divisions \| division	7
Goodwill	$ 423,644	$ 348,811		$ 386,306
Number of reportable segments \| segment	1
Reorganization of geographic regional reporting lines \| Adjustment \| Midwest region
Segment Reporting Information [Line Items]
Goodwill			$ 50,973
Indefinite lived intangibles			5,995
Reorganization of geographic regional reporting lines \| Adjustment \| Central region
Segment Reporting Information [Line Items]
Goodwill			(50,973)
Indefinite lived intangibles			$ (9,480)