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No definition available.

Name:	grbk_BookValueofFinishedLotsandLandUnderDevelopment
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Balance Type:	na
Period Type:	instant

No definition available.

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The revolving credit facility is subject to a borrowing base limitation equal to (1) this percentage times the total value of lots owned, plus (2) a percentage of the total value of land owned by certain of the Company's subsidiaries.

No definition available.

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The revolving credit facility is subject to a borrowing base limitation equal to (1) this percentage times the total value of land, plus (2) a percentage of the total value of lots owned by certain of the Company's subsidiaries.

No definition available.

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No definition available.

Name:	grbk_BorrowingBaseLimitationforUnrestrictedCash
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Debt Instrument, Covenant, Temporary Borrowing Base Waiver, Maximum Loan-to-value Ratio

No definition available.

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Line of Credit Facility, Upfront Fee on Extended Commitments

No definition available.

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Long-term Line of Credit, Increase in Commitment

No definition available.

Name:	grbk_LongtermLineofCreditIncreaseinCommitment
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Balance Type:	credit
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The value of land is restricted from being more than this percentage times the borrowing base.

No definition available.

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No definition available.

Name:	grbk_UnrestrictedCashBorrowingBaseLimitation
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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

No definition available.

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Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 835
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Contractual interest rate for funds borrowed, under the debt agreement.

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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.

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Period Type:	duration

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/2003/role/presentationRef
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Amount of interest payable on debt, including, but not limited to, trade payables.

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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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Name:	us-gaap_LineOfCredit
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Balance Type:	credit
Period Type:	instant

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

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

No definition available.

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Including the current and noncurrent portions, aggregate carrying amount of all types of notes payable, as of the balance sheet date, with initial maturities beyond one year or beyond the normal operating cycle, if longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Name:	us-gaap_NotesPayable
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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Name:	us-gaap_DebtInstrumentAxis=grbk_GrahamMortgageCorporationMember
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Data Type:	na
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Data Type:	na
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Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
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