Interim Financial Statements - Additional Information (Detail) (Cost Of Revenue, USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
May 31, 2013	May 31, 2013
Gross
Interim Reporting [Line Items]
Prior year adjustments	$ 1.9	$ 1.9
Net Of Tax
Interim Reporting [Line Items]
Prior year adjustments	$ 1.6	$ 1.6

Effect on financial statements related to corrections of prior year errors in the current year financial statements when the effect of the prior year error was immaterial to the prior year financial statements and the current year correction is immaterial to the current year financial statements.

No definition available.

Name:	gbx_ImmaterialErrorCorrections
Namespace Prefix:	gbx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration