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Earnest Money Deposits (Schedule of Expected Land Purchase Payments Under Option Agreements) (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Other Restricted Assets [Abstract]    
2015 $ 37,383grbk_LandunderPurchaseOptionsExpectedPurchasePaymentsNextTwelveMonths  
2016 23,269grbk_LandunderPurchaseOptionsExpectedPurchasePaymentsYearTwo  
2017 10,918grbk_LandunderPurchaseOptionsExpectedPurchasePaymentsYearThree  
Total $ 71,570grbk_LandunderPurchaseOptionsExercisePrice $ 61,800grbk_LandunderPurchaseOptionsExercisePrice