Quarterly Results of Operations (Unaudited) - Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended																12 Months Ended
	Aug. 31, 2018		May 31, 2018		Feb. 28, 2018		Nov. 30, 2017		Aug. 31, 2017		May 31, 2017		Feb. 28, 2017		Nov. 30, 2016		Aug. 31, 2018		Aug. 31, 2017		Aug. 31, 2016
Revenue
Revenue	$ 689,206		$ 641,387		$ 629,336		$ 559,535		$ 611,407		$ 439,161		$ 566,282		$ 552,314		$ 2,519,464	[1]	$ 2,169,164	[1]	$ 2,679,524	[1]
Cost of revenue
Cost of revenue	583,319		532,880		523,989		470,221		511,485		349,460		447,357		439,563		2,110,409		1,747,865		2,128,087
Margin	105,887		108,507		105,347		89,314		99,922		89,701		118,925		112,751		409,055		421,299		551,437
Selling and administrative	51,309		51,793		50,294		47,043		47,089		42,810		39,495		41,213		200,439		170,607		158,681
Net gain on disposition of equipment	(4,556)		(14,825)		(5,817)		(19,171)		(4,947)		(1,581)		(2,090)		(1,122)		(44,369)		(9,740)		(15,796)
Earnings from operations	59,134		71,539		60,870		61,442		57,780		48,472		81,520		72,660		252,985		260,432		408,552
Selling and administrative	51,309		51,793		50,294		47,043		47,089		42,810		39,495		41,213		200,439		170,607		158,681
Net gain on disposition of equipment	(4,556)		(14,825)		(5,817)		(19,171)		(4,947)		(1,581)		(2,090)		(1,122)		(44,369)		(9,740)		(15,796)
Earnings from operations	59,134		71,539		60,870		61,442		57,780		48,472		81,520		72,660		252,985		260,432		408,552
Other costs
Interest and foreign exchange	8,786		6,533		7,029		7,020		8,901		7,894		5,673		1,724		29,368		24,192		13,502
Earnings before income tax and earnings (loss) from unconsolidated affiliates	50,348		65,006		53,841		54,422		48,879		40,578		75,847		70,936		223,617		236,240		395,050
Income tax expense	(10,115)		(15,944)		11,301		(18,135)		(10,114)		(8,656)		(24,858)		(20,386)		(32,893)		(64,014)		(112,322)
Earnings (loss) from unconsolidated affiliates	(3,075)		(12,823)		147		(2,910)		(6,511)		(681)		(1,988)		(2,584)		(18,661)		(11,764)		2,096
Net earnings	37,158		36,239		65,289		33,377		32,254		31,241		49,001		47,966		172,063		160,462		284,824
Net earnings attributable to noncontrolling interest	(6,223)		(3,288)		(3,647)		(7,124)		(8,508)		1,582		(14,465)		(23,004)		(20,282)		(44,395)		(101,611)
Net earnings attributable to Greenbrier	$ 30,935		$ 32,951		$ 61,642		$ 26,253		$ 23,746		$ 32,823		$ 34,536		$ 24,962		$ 151,781		$ 116,067		$ 183,213
Basic earnings per common share	$ 0.95	[2]	$ 1.03	[2]	$ 2.10	[2]	$ 0.90	[2]	$ 0.81	[3]	$ 1.12	[3]	$ 1.19	[3]	$ 0.86	[3]	$ 4.92	[2]	$ 3.97	[3]	$ 6.28
Diluted earnings per common share	0.94	[2]	1.01	[2]	1.91	[2]	0.83	[2]	0.75	[3]	1.03	[3]	1.09	[3]	0.79	[3]	4.68	[2],[4]	3.65	[3],[4]	5.73	[4]
Basic earnings per common share	0.95	[2]	1.03	[2]	2.10	[2]	0.90	[2]	0.81	[3]	1.12	[3]	1.19	[3]	0.86	[3]	4.92	[2]	3.97	[3]	6.28
Diluted earnings per common share	$ 0.94	[2]	$ 1.01	[2]	$ 1.91	[2]	$ 0.83	[2]	$ 0.75	[3]	$ 1.03	[3]	$ 1.09	[3]	$ 0.79	[3]	$ 4.68	[2],[4]	$ 3.65	[3],[4]	$ 5.73	[4]
Manufacturing
Revenue
Revenue	$ 571,175		$ 510,099		$ 511,827		$ 451,485		$ 508,547		$ 317,104		$ 445,504		$ 454,033		$ 2,044,586		$ 1,725,188		$ 2,096,331
Cost of revenue
Cost of revenue	489,517		427,875		429,165		380,850		425,531		245,228		346,653		356,555		1,727,407		1,373,967		1,630,554
Earnings from operations																	240,901		295,334		415,094
Earnings from operations																	240,901		295,334		415,094
Wheels, Repair & Parts
Revenue
Revenue	85,787		94,515		88,710		78,011		75,099		85,231		82,714		69,635		347,023		312,679		322,395
Cost of revenue
Cost of revenue	79,266		85,850		80,708		72,506		69,876		77,985		75,497		64,978		318,330		288,336		293,751
Earnings from operations																	16,731		14,984		19,948
Earnings from operations																	16,731		14,984		19,948
Leasing & Services
Revenue
Revenue	32,244		36,773		28,799		30,039		27,761		36,826		38,064		28,646		127,855		131,297		260,798
Cost of revenue
Cost of revenue	$ 14,536		$ 19,155		$ 14,116		$ 16,865		$ 16,078		$ 26,247		$ 25,207		$ 18,030		64,672		85,562		203,782
Earnings from operations																	88,481		31,904		51,723
Earnings from operations																	$ 88,481		$ 31,904		$ 51,723

[1] Revenue is presented on the basis of geographic location of customers.

[2] Quarterly amounts do 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, restricted stock units that are not considered participating securities, restricted stock units that are subject to performance criteria for which actual levels of performance above target have been achieved and the dilutive effect of shares underlying the 2018 Convertible Notes, during the periods in which they were outstanding, using the "if converted" method in which debt issuance and interest costs, net of tax, were added back to net earnings. The 2018 Convertible notes matured on April 1, 2018.

[3] Quarterly amounts do 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, restricted stock units that are subject to performance criteria for which actual levels of performance above target have been achieved 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.

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