Name:	grbk_GrossProfitHomeBuilding
Namespace Prefix:	grbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Gross Profit on Land and Lots

No definition available.

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

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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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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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
Namespace Prefix:	us-gaap_
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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Period Type:	duration

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.

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Balance Type:	na
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Balance Type:
Period Type:

Name:	us-gaap_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
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Name:	us-gaap_StatementGeographicalAxis=stpr_TX
Namespace Prefix:
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