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Earnest Money Deposits (Details) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2014 Lots | Dec. 31, 2013 Lots
Other Restricted Assets [Abstract] |  |
Number of lots under option | 1,082 grbk_LotsunderPurchaseOptionsNumber | 910 grbk_LotsunderPurchaseOptionsNumber
Land not owned under option agreements, exercise price | $ 71,570 grbk_LandunderPurchaseOptionsExercisePrice | $ 61,800 grbk_LandunderPurchaseOptionsExercisePrice

X
- Definition Land under Purchase Options, Exercise Price + References No definition available. + Details
Name: | grbk_LandunderPurchaseOptionsExercisePrice
Namespace Prefix: | grbk_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Lots under Purchase Options, Number + References No definition available. + Details
Name: | grbk_LotsunderPurchaseOptionsNumber
Namespace Prefix: | grbk_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_OtherRestrictedAssetsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration