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Condensed Consolidating Statement of Cash Flows (Parenthetical) (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Nov. 30, 2014
Nov. 30, 2013
Parent    
Condensed Cash Flow Statements, Captions [Line Items]    
Intercompany advances $ (55,267)gbx_PaymentsForProceedsFromIntercompanyAdvancesFromFinancingActivities
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember		 $ (33,902)gbx_PaymentsForProceedsFromIntercompanyAdvancesFromFinancingActivities
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Combined Guarantor Subsidiaries    
Condensed Cash Flow Statements, Captions [Line Items]    
Intercompany advances 55,477gbx_PaymentsForProceedsFromIntercompanyAdvancesFromFinancingActivities
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember		 34,562gbx_PaymentsForProceedsFromIntercompanyAdvancesFromFinancingActivities
/ dei_LegalEntityAxis
= us-gaap_GuarantorSubsidiariesMember
Combined Non-Guarantor Subsidiaries    
Condensed Cash Flow Statements, Captions [Line Items]    
Intercompany advances $ (210)gbx_PaymentsForProceedsFromIntercompanyAdvancesFromFinancingActivities
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember		 $ (660)gbx_PaymentsForProceedsFromIntercompanyAdvancesFromFinancingActivities
/ dei_LegalEntityAxis
= us-gaap_NonGuarantorSubsidiariesMember