Approach to Calculate Diluted Earning Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Feb. 28, 2015		Feb. 28, 2014		Feb. 28, 2015		Feb. 28, 2014
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings attributable to Greenbrier	$ 50,351		$ 15,587		$ 83,137		$ 30,975
Weighted average diluted common shares outstanding	33,073		34,345		33,395		34,404
Diluted earnings per share	$ 1.57	[1]	$ 0.50	[1]	$ 2.57	[1]	$ 0.98	[1]
2018 Senior Notes
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Interest and debt issuance costs on the 2018 Convertible notes, net of tax	1,416		1,416		2,832		2,832
Earnings before interest and debt issuance costs on convertible notes	$ 51,767		$ 17,003		$ 85,969		$ 33,807

[1] Diluted earnings per share was calculated as follows: Earnings before interest and debt issuance costs (net of tax) on convertible notes Weighted average diluted common shares outstanding