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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 1,082grbk_LotsunderPurchaseOptionsNumber 910grbk_LotsunderPurchaseOptionsNumber
Land not owned under option agreements, exercise price $ 71,570grbk_LandunderPurchaseOptionsExercisePrice $ 61,800grbk_LandunderPurchaseOptionsExercisePrice