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. 29, 2020	Feb. 28, 2019	Feb. 29, 2020	Feb. 28, 2019
Earnings Per Share [Abstract]
Net earnings attributable to Greenbrier	$ 13,629	$ 2,765	$ 21,298	$ 20,721
Weighted average diluted common shares outstanding	33,482	33,206	33,382	33,149
Diluted earnings per share	$ 0.41	$ 0.08	$ 0.64	$ 0.63