Name:	grbk_GrossProfitHomeBuilding
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Gross Profit on Land and Lots

No definition available.

Name:	grbk_GrossProfitonLandandLots
Namespace Prefix:	grbk_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Income before taxes on homebuilding operations

No definition available.

Name:	grbk_Incomebeforetaxeshomebuillding
Namespace Prefix:	grbk_
Data Type:	xbrli:monetaryItemType
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Income before taxes on land and lots

No definition available.

Name:	grbk_Incomebeforetaxesonlandandlots
Namespace Prefix:	grbk_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1,2)
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Name:	us-gaap_GrossProfit
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Revenue related to the sale of homes and home building activities including design, development, general contracting, and renovation services for residential buildings, including single-family houses, multifamily housing, townhouses, apartments, and modular housing.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Name:	us-gaap_HomeBuildingRevenue
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Data Type:	xbrli:monetaryItemType
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This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=51673353&loc=d3e41242-110953

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

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 10
-Article 5

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Total of (1) improvements, (2) held-for-sale, (3) land and land under development, (4) construction-in-process, (5) mortgage loans held-in-inventory, and (6) other real estate investments which are considered inventory due to being held for sale or disposition.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Revenue from the sale of land in the reporting period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Name:	us-gaap_LandSales
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Revenue from the sale of commercial, industrial, or residential property during the period. This element is more likely than not relevant to an entity for which real estate operations are a principal activity. If real estate operations are not a principal activity, the reporting entity would likely use a gain (loss) on sale of property, plant, or equipment type element.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Name:	us-gaap_SalesOfRealEstate
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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_SegmentReportingInformationLineItems
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Data Type:	xbrli:stringItemType
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Period Type:	duration

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Name:	us-gaap_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
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Name:	us-gaap_StatementBusinessSegmentsAxis=grbk_BuilderOperationsMember
Namespace Prefix:
Data Type:	na
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Name:	us-gaap_StatementBusinessSegmentsAxis=stpr_TX
Namespace Prefix:
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Name:	us-gaap_StatementBusinessSegmentsAxis=stpr_GA
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