Approach to Calculate Diluted Earning Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended																12 Months Ended
	Aug. 31, 2012		May 31, 2012		Feb. 29, 2012		Nov. 30, 2011		Aug. 31, 2011		May 31, 2011		Feb. 28, 2011		Nov. 30, 2010		Aug. 31, 2012		Aug. 31, 2011		Aug. 31, 2010
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings attributable to Greenbrier	$ 7,404		$ 19,117		$ 17,670		$ 14,517		$ 12,634		$ (3,314)		$ (550)		$ (2,304)		$ 58,708		$ 6,466		$ 4,277
Earnings before interest and debt issuance costs on convertible notes																	$ 64,385,000
Weighted average diluted common shares outstanding																	33,718		26,501		20,213
Diluted earnings per share	$ 0.26	[1]	$ 0.61	[1]	$ 0.57	[1]	$ 0.48	[1]	$ 0.42	[2]	$ (0.14)	[2]	$ (0.02)	[2]	$ (0.11)	[2]	$ 1.91	[1],[3]	$ 0.24	[2]	$ 0.21
2026 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																	$ 5,677

[1] Quarterly amounts do not total to the year to date amount as each period is calculated discretely. Dilutive earnings per common share includes the outstanding warrants using the treasury stock method and the dilutive effect of shares underlying the 2018 Convertible Notes using the "if converted" method in which debt issuance and interest costs, net of tax, were added back to net earnings.

[2] Quarterly amounts do not total to the year to date amount as each period is calculated discretely. The dilutive effect of warrants is excluded from per share calculations for the first, second and third quarters due to net loss for those periods. The fourth quarter dilutive earnings per common share includes the outstanding warrants using the treasury stock method, which equates to 2.3 million shares, and the dilutive effect of 6.0 million shares underlying the 2018 Convertible Notes using the "if converted" method under which $1.4 million of debt issuance and interest costs, net of tax, were added back to net earnings.

[3] Diluted earnings per share was calculated as follows: Earnings before interest and debt issuance costs on convertible notes Weighted average diluted common shares outstanding