Leased Railcars for Syndication - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	May 31, 2013	Aug. 31, 2012
Leased Railcars For Syndication [Line Items]
Leased railcars for syndication	$ 71,091	$ 97,798

Leased Railcars for Syndication, at Carrying Value

No definition available.

Name:	gbx_LeasedRailcarsForSyndicationAtCarryingValue
Namespace Prefix:	gbx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant