Quarterly Results of Operations (Detail) - USD ($) $ / shares in Units, $ 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
Revenue
Revenues	$ 611,407		$ 439,161		$ 566,282		$ 552,314		$ 595,190		$ 612,866		$ 669,079		$ 802,389		$ 2,169,164	[1]	$ 2,679,524	[1]	$ 2,605,278	[1]
Cost of revenue
Cost of revenue	511,485		349,460		447,357		439,563		475,507		485,768		549,188		617,624		1,747,865		2,128,087		2,067,925
Margin	99,922		89,701		118,925		112,751		119,683		127,098		119,891		184,765		421,299		551,437		537,353
Selling and administrative	47,089		42,810		39,495		41,213		40,608		43,280		38,244		36,549		170,607		158,681		151,791
Net gain on disposition of equipment	(4,947)		(1,581)		(2,090)		(1,122)		(4,470)		(311)		(10,746)		(269)		(9,740)		(15,796)		(1,330)
Earnings from operations	57,780		48,472		81,520		72,660		83,545		84,129		92,393		148,485		260,432		408,552		386,892
Selling and administrative	47,089		42,810		39,495		41,213		40,608		43,280		38,244		36,549		170,607		158,681		151,791
Net gain on disposition of equipment	(4,947)		(1,581)		(2,090)		(1,122)		(4,470)		(311)		(10,746)		(269)		(9,740)		(15,796)		(1,330)
Earnings from operations	57,780		48,472		81,520		72,660		83,545		84,129		92,393		148,485		260,432		408,552		386,892
Other costs
Interest and foreign exchange	8,901		7,894		5,673		1,724		2,937		3,712		1,417		5,436		24,192		13,502		11,179
Earnings before income tax and earnings (loss) from unconsolidated affiliates	48,879		40,578		75,847		70,936		80,608		80,417		90,976		143,049		236,240		395,050		375,713
Income tax expense	(10,114)		(8,656)		(24,858)		(20,386)		(19,420)		(22,449)		(25,734)		(44,719)		(64,014)		(112,322)		(112,160)
Earnings (loss) from unconsolidated affiliates	(6,511)		(681)		(1,988)		(2,584)		(825)		1,564		974		383		(11,764)		2,096		1,756
Net earnings	32,254		31,241		49,001		47,966		60,363		59,532		66,216		98,713		160,462		284,824		265,309
Net earnings attributable to noncontrolling interest	(8,508)		1,582		(14,465)		(23,004)		(26,803)		(24,180)		(21,348)		(29,280)		(44,395)		(101,611)		(72,477)
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
Basic earnings per common share	$ 0.81	[2]	$ 1.12	[2]	$ 1.19	[2]	$ 0.86	[2]	$ 1.15	[3]	$ 1.22	[3]	$ 1.54	[3]	$ 2.36	[3]	$ 3.97	[2]	$ 6.28	[3]	$ 6.85
Diluted earnings per common share	0.75	[2]	1.03	[2]	1.09	[2]	0.79	[2]	1.06	[3]	1.12	[3]	1.41	[3]	2.15	[3]	3.65	[2],[4]	5.73	[3],[4]	5.93	[4]
Basic earnings per common share	0.81	[2]	1.12	[2]	1.19	[2]	0.86	[2]	1.15	[3]	1.22	[3]	1.54	[3]	2.36	[3]	3.97	[2]	6.28	[3]	6.85
Diluted earnings per common share	$ 0.75	[2]	$ 1.03	[2]	$ 1.09	[2]	$ 0.79	[2]	$ 1.06	[3]	$ 1.12	[3]	$ 1.41	[3]	$ 2.15	[3]	$ 3.65	[2],[4]	$ 5.73	[3],[4]	$ 5.93	[4]
Manufacturing
Revenue
Revenues	$ 508,547		$ 317,104		$ 445,504		$ 454,033		$ 484,645		$ 458,494		$ 454,531		$ 698,661		$ 1,725,188		$ 2,096,331		$ 2,136,051
Cost of revenue
Cost of revenue	425,531		245,228		346,653		356,555		382,919		352,775		361,827		533,033		1,373,967		1,630,554		1,691,414
Earnings from operations																	295,334		415,094		396,921
Earnings from operations																	295,334		415,094		396,921
Wheels & Parts
Revenue
Revenues	75,099		85,231		82,714		69,635		74,791		78,417		90,458		78,729		312,679		322,395		371,237
Cost of revenue
Cost of revenue	69,876		77,985		75,497		64,978		69,543		69,818		81,388		73,002		288,336		293,751		334,680
Earnings from operations																	14,984		19,948		27,563
Earnings from operations																	14,984		19,948		27,563
Leasing & Services
Revenue
Revenues	27,761		36,826		38,064		28,646		35,754		75,955		124,090		24,999		131,297		260,798		97,990
Cost of revenue
Cost of revenue	$ 16,078		$ 26,247		$ 25,207		$ 18,030		$ 23,045		$ 63,175		$ 105,973		$ 11,589		85,562		203,782		41,831
Earnings from operations																	31,904		51,723		41,887
Earnings from operations																	$ 31,904		$ 51,723		$ 41,887

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

[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 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.

[3] 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.

[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