Condensed Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock Shares	Additional Paid-in Capital	Additional Paid-in Capital Cumulative Effect Adjustment Due to Adoption	Retained Earnings	Retained Earnings Cumulative Effect Adjustment Due to Adoption	Accumulated Other Comprehensive (Loss)	Total Equity - Greenbrier	Total Equity - Greenbrier Cumulative Effect Adjustment Due to Adoption	Noncontrolling Interest	Equity Excluding Contingently Redeemable Noncontrolling Interest	Equity Excluding Contingently Redeemable Noncontrolling Interest Cumulative Effect Adjustment Due to Adoption	Contingently Redeemable Noncontrolling Interest
Beginning balance at Aug. 31, 2021			$ 469.7	$ (58.9)	$ 881.7	$ 4.9	$ (43.7)	$ 1,307.7	$ (54.0)	$ 168.7	$ 1,476.4	$ (54.0)
Beginning balance (in shares) at Aug. 31, 2021		32,400
Beginning balance at Aug. 31, 2021													$ 29.7
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate202006Member		us-gaap:AccountingStandardsUpdate202006Member			us-gaap:AccountingStandardsUpdate202006Member			us-gaap:AccountingStandardsUpdate202006Member
Net earnings	$ 24.4				$ 26.7			$ 26.7		(0.4)	$ 26.3		(1.9)
Other comprehensive income, net	7.2						7.1	7.1		0.1	7.2
Noncontrolling interest adjustments			$ 2.2					2.2		(1.5)	0.7
Joint venture partner distribution declared										(10.1)	(10.1)
Restricted stock awards (net of cancellations)			11.9					11.9			11.9
Restricted stock awards (net of cancellations) (in shares)		200
Unamortized restricted stock			(15.3)					(15.3)			(15.3)
Stock based compensation expense			10.9					10.9			10.9
Cash dividends					(26.8)			(26.8)			(26.8)
Ending balance at May. 31, 2022			420.5		886.5		(36.6)	1,270.4		156.8	1,427.2
Ending Balance (in shares) at May. 31, 2022		32,600
Ending Balance at May. 31, 2022													27.8
Beginning balance at Feb. 28, 2022			$ 413.4	$ (0.1)	892.5		(53.3)	$ 1,252.6	$ (0.1)	154.1	$ 1,406.7	$ (0.1)
Beginning balance (in shares) at Feb. 28, 2022		32,600
Beginning balance at Feb. 28, 2022													28.5
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate202006Member					us-gaap:AccountingStandardsUpdate202006Member			us-gaap:AccountingStandardsUpdate202006Member
Net earnings	7.6				3.1			$ 3.1		5.2	$ 8.3		(0.7)
Other comprehensive income, net	16.8						16.7	16.7		0.1	16.8
Noncontrolling interest adjustments			$ 2.2					2.2		(0.9)	1.3
Joint venture partner distribution declared										(1.7)	(1.7)
Stock based compensation expense			5.0					5.0			5.0
Cash dividends					(9.1)			(9.1)			(9.1)
Ending balance at May. 31, 2022			420.5		886.5		(36.6)	1,270.4		156.8	1,427.2
Ending Balance (in shares) at May. 31, 2022		32,600
Ending Balance at May. 31, 2022													27.8
Beginning balance at Aug. 31, 2022	$ 1,429.1		424.8		897.7		(45.6)	1,276.9		152.2	1,429.1
Beginning balance (in shares) at Aug. 31, 2022	32,603	32,600
Beginning balance at Aug. 31, 2022													27.7
Net earnings	$ 46.2				37.7			37.7		8.4	46.1		0.1
Other comprehensive income, net	22.0						22.0	22.0			22.0
Noncontrolling interest adjustments			(7.9)		(26.3)			(34.2)		(1.6)	(35.8)		26.3
Joint venture partner distribution declared										(10.9)	(10.9)
Restricted stock awards (net of cancellations)			8.9					8.9			8.9
Restricted stock awards (net of cancellations) (in shares)		200
Unamortized restricted stock			(11.1)					(11.1)			(11.1)
Stock based compensation expense			8.8					8.8			8.8
Repurchase of stock	$ (49.4)		(49.4)					(49.4)			(49.4)
Repurchase of stock (in shares)	(1,700)	(1,700)
Cash dividends					(26.9)			(26.9)			(26.9)
Ending balance at May. 31, 2023	$ 1,380.8		374.1		882.2		(23.6)	1,232.7		148.1	1,380.8
Ending Balance (in shares) at May. 31, 2023	31,111	31,100
Ending Balance at May. 31, 2023													54.1
Beginning balance at Feb. 28, 2023			403.0		896.0		(21.7)	1,277.3		144.6	1,421.9
Beginning balance (in shares) at Feb. 28, 2023		32,300
Beginning balance at Feb. 28, 2023													27.5
Net earnings	$ 26.7				21.3			21.3		5.1	26.4		0.3
Other comprehensive income, net	(1.9)						(1.9)	(1.9)			(1.9)
Noncontrolling interest adjustments					(26.3)			(26.3)		0.4	(25.9)		26.3
Joint venture partner distribution declared										(2.0)	(2.0)
Restricted stock awards (net of cancellations)			(0.1)					(0.1)			(0.1)
Unamortized restricted stock			0.3					0.3			0.3
Stock based compensation expense			2.9					2.9			2.9
Repurchase of stock	$ (32.0)		(32.0)					(32.0)			(32.0)
Repurchase of stock (in shares)	(1,200)	(1,200)
Cash dividends					(8.8)			(8.8)			(8.8)
Ending balance at May. 31, 2023	$ 1,380.8		$ 374.1		$ 882.2		$ (23.6)	$ 1,232.7		$ 148.1	$ 1,380.8
Ending Balance (in shares) at May. 31, 2023	31,111	31,100
Ending Balance at May. 31, 2023													$ 54.1