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Reconciliation of Basic and Diluted Earnings Per Common Share (Parenthetical) (Detail) (2026 Senior Notes, USD $)
Nov. 30, 2014
Nov. 30, 2013
2026 Senior Notes
   
Earnings Per Share Disclosure [Line Items]    
Convertible notes average stock price, per share $ 48.05us-gaap_DebtInstrumentConvertibleConversionPrice1
/ us-gaap_LongtermDebtTypeAxis
= gbx_SeniorNotesDueTwentyTwentySixMember
$ 48.05us-gaap_DebtInstrumentConvertibleConversionPrice1
/ us-gaap_LongtermDebtTypeAxis
= gbx_SeniorNotesDueTwentyTwentySixMember