Name:	dei_DocumentPeriodEndDate
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Amount, after accumulated amortization, of debt issuance costs related to line of credit arrangements. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 835
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Name:	us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet
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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 835
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-Topic 835
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-Topic 470
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Balance Type:	debit
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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 944
-SubTopic 605
-Name Accounting Standards Codification
-Section 55
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Balance Type:	credit
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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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-Topic 944
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Name:	us-gaap_LineOfCredit
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Date the credit facility terminates, in YYYY-MM-DD format.

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-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
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-Subparagraph (SX 210.5-02(19)(b))
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Balance Type:	na
Period Type:	duration

The effective interest rate at the end of the reporting period.

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Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

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.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 235
-SubTopic 10
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-Topic 235
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(f))
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-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
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-Paragraph 6
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-Topic 470
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Name:	us-gaap_LineOfCreditFacilityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 470
-SubTopic 10
-Name Accounting Standards Codification
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-Subparagraph (SX 210.5-02(22)(b))
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Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
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Balance Type:	credit
Period Type:	instant

The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
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Carrying value as of the balance sheet date of the outstanding short-term borrowings under a revolving line of credit used by mortgage bankers to finance the origination or purchase of loans.

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Name:	us-gaap_WarehouseAgreementBorrowings
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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Name:	us-gaap_CreditFacilityAxis=us-gaap_WarehouseAgreementBorrowingsMember
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Name:	us-gaap_CreditFacilityAxis=grbk_WarehouseFacilityExpiringOctober312025Member
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Name:	us-gaap_CreditFacilityAxis=grbk_WarehouseFacilityExpiringDecember182025Member
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Data Type:	na
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Name:	us-gaap_DebtInstrumentAxis=us-gaap_RevolvingCreditFacilityMember
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Data Type:	na
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Name:	us-gaap_DebtInstrumentAxis=us-gaap_UnsecuredDebtMember
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Name:	us-gaap_DebtInstrumentAxis=us-gaap_WarehouseAgreementBorrowingsMember
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