Earnings Per Share - Approach to Calculate Diluted Earning Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Nov. 30, 2019	Nov. 30, 2018
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings attributable to Greenbrier	$ 7,669	$ 17,956
Weighted average diluted common shares outstanding	33,284	33,093
Diluted earnings per share	$ 0.23	$ 0.54