Consolidated Statements of Equity - USD ($) $ in Millions	Total	Common Stock Shares	Additional Paid-in Capital	Additional Paid-in Capital Cumulative Effect Adjustment Due to Adoption	Additional Paid-in Capital 2.875% Convertible senior notes, due 2028	Additional Paid-in Capital 2.875% Convertible senior notes, due 2024	Additional Paid-in Capital 2.25% Convertible senior notes, due 2024	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	Total Equity - Greenbrier 2.875% Convertible senior notes, due 2028	Total Equity - Greenbrier 2.875% Convertible senior notes, due 2024	Total Equity - Greenbrier 2.25% Convertible senior notes, due 2024	Noncontrolling Interest	Equity Excluding Contingently Redeemable Noncontrolling Interest	Equity Excluding Contingently Redeemable Noncontrolling Interest Cumulative Effect Adjustment Due to Adoption	Equity Excluding Contingently Redeemable Noncontrolling Interest 2.875% Convertible senior notes, due 2028	Equity Excluding Contingently Redeemable Noncontrolling Interest 2.875% Convertible senior notes, due 2024	Equity Excluding Contingently Redeemable Noncontrolling Interest 2.25% Convertible senior notes, due 2024	Contingently Redeemable Noncontrolling Interest
Beginning balance at Aug. 31, 2020			$ 460.4					$ 885.5	$ (0.5)	$ (52.8)	$ 1,293.1	$ (0.5)				$ 180.0	$ 1,473.1	$ (0.5)
Beginning balance (in shares) at Aug. 31, 2020		32,700,000
Beginning balance at Aug. 31, 2020																						$ 31.1
Accounting Standards Update [Extensible List]								ASU 2016-13			ASU 2016-13						ASU 2016-13
Net earnings	$ 35.1							$ 32.4			$ 32.4					4.1	$ 36.5					(1.4)
Other comprehensive income (loss), net	9.1									9.1	9.1						9.1
Noncontrolling interest adjustments																2.2	2.2
Joint venture partner distribution declared																(24.6)	(24.6)
Investment by joint venture partner																7.0	7.0
Restricted stock awards (net of cancellations)			13.5								13.5						13.5
Restricted stock awards (net of cancellations) (in shares)		200,000
Unamortized restricted stock			(16.8)								(16.8)						(16.8)
Restricted stock amortization/Stock based compensation expense			14.7								14.7						14.7
Repurchase of stock	(20.0)		(20.0)								(20.0)						(20.0)
Repurchase of stock (in shares)		(500,000)
Convertible Senior Notes, equity component, net of tax					$ 56.3		$ (7.4)						$ 56.3		$ (7.4)				$ 56.3		$ (7.4)
Convertible senior notes,due 2028 issuance costs - equitycomponent, net of tax					$ (1.8)								$ (1.8)						$ (1.8)
Convertible senior notes,due 2024 - equity componentextinguishment, net of tax						$ (29.2)								$ (29.2)						$ (29.2)
Cash dividends								(35.7)			(35.7)						(35.7)
Ending 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)
Ending Balance (in shares) at Aug. 31, 2021		32,400,000
Ending Balance at Aug. 31, 2021																						29.7
Accounting Standards Update [Extensible List]			Accounting Standards Update 2020-06					Accounting Standards Update 2020-06			Accounting Standards Update 2020-06						Accounting Standards Update 2020-06
Net earnings	53.8							$ 46.9			$ 46.9					8.9	$ 55.8					(2.0)
Other comprehensive income (loss), net	(1.9)									(1.9)	(1.9)						(1.9)
Noncontrolling interest adjustments			$ 2.2								2.2					(6.2)	(4.0)
Joint venture partner distribution declared																(19.2)	(19.2)
Restricted stock awards (net of cancellations)			11.3								11.3						11.3
Restricted stock awards (net of cancellations) (in shares)		200,000
Unamortized restricted stock			(15.0)								(15.0)						(15.0)
Restricted stock amortization/Stock based compensation expense			15.5								15.5						15.5
Cash dividends								(35.8)			(35.8)						(35.8)
Ending balance at Aug. 31, 2022	$ 1,429.1		424.8					897.7		(45.6)	1,276.9					152.2	1,429.1
Ending Balance (in shares) at Aug. 31, 2022	32,603,000	32,600,000
Ending Balance at Aug. 31, 2022																						27.7
Net earnings	$ 75.6							62.5			62.5					11.5	74.0					1.6
Other comprehensive income (loss), net	38.3									38.3	38.3						38.3
Noncontrolling interest adjustments			(12.5)					(26.3)			(38.8)					2.8	(36.0)					26.3
Joint venture partner distribution declared																(10.9)	(10.9)
Restricted stock awards (net of cancellations)			8.8								8.8						8.8
Restricted stock awards (net of cancellations) (in shares)		200,000
Unamortized restricted stock			(11.4)								(11.4)						(11.4)
Restricted stock amortization/Stock based compensation expense			12.1								12.1						12.1
Repurchase of stock	$ (56.9)		(57.4)								(57.4)						(57.4)
Repurchase of stock (in shares)	(1,900,000)	(1,900,000)
Cash dividends								(36.4)			(36.4)						(36.4)
Ending balance at Aug. 31, 2023	$ 1,410.2		$ 364.4					$ 897.5		$ (7.3)	$ 1,254.6					$ 155.6	$ 1,410.2
Ending Balance (in shares) at Aug. 31, 2023	30,880,000	30,900,000
Ending Balance at Aug. 31, 2023																						$ 55.6