Approach to Calculate Diluted Earning Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended																12 Months Ended
	Aug. 31, 2017		May 31, 2017		Feb. 28, 2017		Nov. 30, 2016		Aug. 31, 2016		May 31, 2016		Feb. 28, 2016		Nov. 30, 2015		Aug. 31, 2017		Aug. 31, 2016		Aug. 31, 2015
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings attributable to Greenbrier	$ 23,746		$ 32,823		$ 34,536		$ 24,962		$ 33,560		$ 35,352		$ 44,868		$ 69,433		$ 116,067		$ 183,213		$ 192,832
Earnings before interest and debt issuance costs on convertible notes																	$ 118,999		$ 185,908		$ 197,650
Weighted average diluted common shares outstanding																	32,562		32,468		33,328
Diluted earnings per share	$ 0.75	[1]	$ 1.03	[1]	$ 1.09	[1]	$ 0.79	[1]	$ 1.06	[2]	$ 1.12	[2]	$ 1.41	[2]	$ 2.15	[2]	$ 3.65	[1],[3]	$ 5.73	[2],[3]	$ 5.93	[3]
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																	$ 2,932		$ 2,695		$ 4,818

[1] Quarterly amounts may not total to the year to date amount as each period is calculated discretely. Diluted earnings per common share includes the dilutive effect of the 2024 Convertible Notes using the treasury stock method when dilutive 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 may not total to the year to date amount as each period is calculated discretely. Diluted earnings per common share includes the dilutive effect of the 2026 Convertible Notes using the treasury stock method when dilutive 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.

[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