Name:	grbk_ContractPriceEmployeeDiscountPremium
Namespace Prefix:	grbk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Cost of Land and Lots Sales

+ References

No definition available.

+ Details

Name:	grbk_CostofLandandLotsSales
Namespace Prefix:	grbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Equity Method Investment, Ownership Percentage by Partner

+ References

No definition available.

+ Details

Name:	grbk_EquityMethodInvestmentOwnershipPercentagbyPartner
Namespace Prefix:	grbk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The Company's portion of payments for capital contributions

+ References

No definition available.

+ Details

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

- Definition

Percentage of Voting Interest

+ References

No definition available.

+ Details

Name:	grbk_PercentageofVotingInterest
Namespace Prefix:	grbk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

PercentofCentreLivingOperationsConsolidated

+ References

No definition available.

+ Details

Name:	grbk_PercentofCentreLivingOperationsConsolidated
Namespace Prefix:	grbk_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Total estimated capital contributions

+ References

No definition available.

+ Details

Name:	grbk_TotalestimatedCapitalContributions
Namespace Prefix:	grbk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

For an unclassified balance sheet, amount of receivables arising from transactions with related parties.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(1))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39622-107864

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(3))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864

Reference 6: 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(3)(a)(2))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- 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

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

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ 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

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

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The current amount of expenditures for a real estate project that has not yet been completed.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.10)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

+ Details

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

- Definition

Percentage investment held by members or limited partners of limited liability company (LLC) or limited partnership (LP).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

+ Details

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

- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which is directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent (that is, noncontrolling interest, previously referred to as minority interest).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(22))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(24))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.31)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

+ Details

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

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

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

- Definition

The number of real estate properties owned as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfRealEstateProperties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of units in a real estate property owned as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfUnitsInRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Rental expense for the reporting period incurred under operating leases, including minimum and any contingent rent expense, net of related sublease income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41499-112717

+ Details

Name:	us-gaap_OperatingLeasesRentExpenseNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Cash outflow related to amounts given in advance to show or confirm an intention to complete an acquisition of land, buildings, other structures, or any item classified as real estate.

+ References

No definition available.

+ Details

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

- Definition

The cash outflow from the acquisition of residential property intended to generate income for the owner.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3213-108585

+ Details

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

- Definition

Cash received for the sale of real estate that is not part of an investing activity during the current period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

+ Details

Name:	us-gaap_ProceedsFromSaleOfRealEstate
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of deposits held by the entity for a related party (entity, shareholder, employee).

+ References

+ Details

Name:	us-gaap_RelatedPartyDepositLiabilities
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

Name:	us-gaap_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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_RelatedPartyTransactionsByRelatedPartyAxis=grbk_CentreLivingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_IncomeStatementLocationAxis=us-gaap_SellingGeneralAndAdministrativeExpensesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=grbk_ReverseRecapitalizationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_MajorityShareholderMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=grbk_SuwaneeStationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_InvesteeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=grbk_TheParcatCogburnMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=grbk_AcademyStreetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=grbk_GlensatSugarloafMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=grbk_DunwoodyTowneshipMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesInventoryAxis=grbk_DevelopedLotsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PublicUtilitiesInventoryAxis=grbk_TownhomeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=us-gaap_OfficerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CounterpartyNameAxis=grbk_RichardA.CostelloMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CounterpartyNameAxis=grbk_JedDolsonMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Related Party Transactions (Details)					1 Months Ended			3 Months Ended	6 Months Ended	12 Months Ended
Related Party Transactions (Details)	Jun. 10, 2016 USD ($) Lots townhome	Mar. 01, 2016 USD ($)	Jul. 01, 2015 USD ($)	Oct. 27, 2014 USD ($)	Feb. 28, 2017 USD ($)	Jun. 30, 2016 USD ($) Lots	Nov. 30, 2015 USD ($) Lots townhome	Dec. 31, 2017 USD ($) Lots board_seat	Jun. 30, 2017 USD ($) Lots	Dec. 31, 2017 USD ($) Lots board_seat	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Mar. 30, 2016 Lots townhome	Oct. 28, 2015	Sep. 30, 2015 Lots townhome
Related Party Transaction [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent								50.00%		50.00%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners								50.00%		50.00%
Stockholders' Equity Attributable to Noncontrolling Interest								$ 16,691,000		$ 16,691,000	$ 16,913,000
Repayments of Secured Debt										$ 0	0	$ 150,000,000
Percentage of Voting Interest								51.00%		51.00%
Centre Living
Related Party Transaction [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent								50.00%		50.00%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners								50.00%		50.00%
Stockholders' Equity Attributable to Noncontrolling Interest								$ 100,000		$ 100,000	300,000
Percentage of Voting Interest								51.00%		51.00%
PercentofCentreLivingOperationsConsolidated										100.00%
Selling, General and Administrative Expenses
Related Party Transaction [Line Items]
Rent expense										$ 800,000	700,000	600,000
Reverse Recapitalization \| Term Loan Facility \| Secured Debt \| Greenlight Capital, Inc
Related Party Transaction [Line Items]
Debt instrument, term				5 years
Debt instrument, face amount				$ 150,000,000
Stated interest rate				9.00%										10.00%
Repayments of Secured Debt			$ 154,900,000
Percentage of Voting Interest				47.70%
Suwanee Station [Member]
Related Party Transaction [Line Items]
Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest										80.00%
Suwanee Station [Member] \| The Providence Group
Related Party Transaction [Line Items]
Total estimated Capital Contributions								$ 3,400,000		$ 3,400,000
BoardSeatsAvailable \| board_seat								3		3
CapitalContributionsMade										$ 700,000	1,800,000
PaymentsForCapitalContributions										$ 400,000	900,000
BoardSeatsHeld \| board_seat								2		2
Number of lots purchased \| townhome													73
Equity Method Investment, Ownership Percentage													50.00%
EquityMethodInvestment,OwnershipPercentagbyPartner													50.00%
The Parc at Cogburn [Member] \| The Providence Group
Related Party Transaction [Line Items]
Number of townhomes in community \| townhome															19
Number of lots purchased \| Lots									19						11
Payments to acquire residential real estate									$ 1,000,000		300,000	1,800,000
Academy Street [Member]
Related Party Transaction [Line Items]
CapitalContributionsMade										$ 500,000	11,200,000
PaymentsForCapitalContributions										$ 400,000	9,000,000
Academy Street [Member] \| The Providence Group
Related Party Transaction [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent													80.00%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners													20.00%
Number of lots purchased \| Lots													83
Glens at Sugarloaf [Member] \| The Providence Group
Related Party Transaction [Line Items]
Number of townhomes in community \| townhome							92						80
Number of lots purchased \| Lots							12
Payments for deposits on real estate acquisitions							$ 0
Payments to acquire residential real estate		$ 4,800,000										$ 1,000,000
Dunwoody Towneship [Member] \| The Providence Group
Related Party Transaction [Line Items]
Number of townhomes in community \| townhome	40
Number of lots purchased \| Lots	14							26		26
Payments for deposits on real estate acquisitions	$ 0
Payments to acquire residential real estate	$ 1,800,000									$ 3,300,000
Developed Lots [Member] \| Centre Living
Related Party Transaction [Line Items]
ContractPriceEmployeeDiscountPremium										13.00%
Number of lots purchased \| Lots						1
Proceeds from Sale of Real Estate						$ 400,000
Cost of Land and Lots Sales						$ 300,000
Development in Process								$ 600,000		$ 600,000
Accounts receivable due from related party								0		$ 0	$ 100,000
townhome [Member] \| Officer [Member]
Related Party Transaction [Line Items]
ContractPriceEmployeeDiscountPremium					13.00%
Richard A. Costello [Member] \| Centre Living
Related Party Transaction [Line Items]
Proceeds from Sale of Real Estate								495,000
Related Party Deposit Liabilities					$ 110,000
Jed Dolson [Member] \| Centre Living
Related Party Transaction [Line Items]
Proceeds from Sale of Real Estate								$ 472,000
Related Party Deposit Liabilities					$ 110,000