Earnings Per Share - Approach to Calculate Diluted Earning Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Feb. 28, 2019	Feb. 28, 2018	Feb. 28, 2019	Feb. 28, 2018
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings attributable to Greenbrier	$ 2,765	$ 61,642	$ 20,721	$ 87,895
Weighted average diluted common shares outstanding	33,206	32,711	33,149	32,703
Diluted earnings per share	$ 0.08	$ 1.91	$ 0.63	$ 2.74
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		$ 843		$ 1,686
Earnings before interest and debt issuance costs on 2018 Convertible Notes		$ 62,485		$ 89,581