Condensed Consolidated Statements of Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock Shares	Additional Paid-in Capital	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	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 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	Total Equity - Greenbrier Cumulative Effect Adjustment Due to Adoption	Noncontrolling Interest	Equity Excluding Contingently Redeemable Noncontrolling Interest	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	Equity Excluding Contingently Redeemable Noncontrolling Interest Cumulative Effect Adjustment Due to Adoption	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
Beginning balance at Aug. 31, 2020																						$ 31.1
Accounting Standards Update [Extensible List]								ASU 2016-13			ASU 2016-13						ASU 2016-13
Net earnings	$ (0.5)							$ 0.7			$ 0.7					(0.4)	$ 0.3					(0.8)
Other comprehensive income, net	$ 12.8									12.8	12.8						12.8
Noncontrolling interest adjustments																0.3	0.3
Joint venture partner distribution declared																(23.0)	(23.0)
Investment by joint venture partner																7.0	7.0
Restricted stock awards (net of cancellations)			15.0								15.0						15.0
Restricted stock awards (net of cancellations) (in shares)		100
Unamortized restricted stock			(17.9)								(17.9)						(17.9)
Restricted stock amortization			12.5								12.5						12.5
Repurchase of stock			(20.0)								(20.0)						(20.0)
Repurchase of stock (in shares)		(400)
Convertible senior notes, due 2028 - equity component, net of tax				$ 56.3								$ 56.3						$ 56.3
Convertible senior notes, due 2028 issuance costs - equity component, net of tax				(1.8)								(1.8)						(1.8)
Convertible senior notes, due 2024 - equity component extinguishment, net of tax					$ (28.5)	$ (8.2)							$ (28.5)	$ (8.2)					$ (28.5)	$ (8.2)
Cash dividends								(26.7)			(26.7)						(26.7)
Ending balance at May. 31, 2021			467.8					859.0		(40.0)	1,286.8					163.9	1,450.7
Ending Balance (in shares) at May. 31, 2021		32,400
Ending Balance at May. 31, 2021																						30.3
Beginning balance at Feb. 28, 2021			467.0					848.2		(46.7)	1,268.5					175.9	1,444.4
Beginning balance (in shares) at Feb. 28, 2021	32,800
Beginning balance at Feb. 28, 2021																						30.0
Net earnings	$ 20.0							19.7			19.7						19.7					0.3
Other comprehensive income, net	6.7									6.7	6.7						6.7
Noncontrolling interest adjustments																1.6	1.6
Joint venture partner distribution declared																(20.6)	(20.6)
Investment by joint venture partner																7.0	7.0
Restricted stock awards (net of cancellations)			(0.5)								(0.5)						(0.5)
Restricted stock amortization			3.5								3.5						3.5
Repurchase of stock			(20.0)								(20.0)						(20.0)
Repurchase of stock (in shares)		(400)
Convertible senior notes, due 2028 - equity component, net of tax				56.3								56.3						56.3
Convertible senior notes, due 2028 issuance costs - equity component, net of tax				$ (1.8)								$ (1.8)						$ (1.8)
Convertible senior notes, due 2024 - equity component extinguishment, net of tax					$ (28.5)	$ (8.2)							$ (28.5)	$ (8.2)					$ (28.5)	$ (8.2)
Cash dividends								(8.9)			(8.9)
Ending balance at May. 31, 2021			467.8					859.0		(40.0)	1,286.8					163.9	1,450.7
Ending Balance (in shares) at May. 31, 2021		32,400
Ending Balance at May. 31, 2021																						30.3
Beginning balance at Aug. 31, 2021	$ 1,476.4		$ 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	32,397	32,400
Beginning balance at Aug. 31, 2021																						29.7
Accounting Standards Update [Extensible List]			ASU 2020-06					ASU 2020-06			ASU 2020-06						ASU 2020-06
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)
Restricted stock amortization			10.9								10.9						10.9
Cash dividends								(26.8)			(26.8)						(26.8)
Ending balance at May. 31, 2022	$ 1,427.2	$ 32.6	420.5					886.5		(36.6)	1,270.4					156.8	1,427.2
Ending Balance (in shares) at May. 31, 2022	32,588	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]			ASU 2020-06								ASU 2020-06						ASU 2020-06
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)
Restricted stock amortization			$ 5.0								5.0						5.0
Cash dividends								(9.1)			(9.1)						(9.1)
Ending balance at May. 31, 2022	$ 1,427.2	$ 32.6	$ 420.5					$ 886.5		$ (36.6)	$ 1,270.4					$ 156.8	$ 1,427.2
Ending Balance (in shares) at May. 31, 2022	32,588	32,600
Ending Balance at May. 31, 2022																						$ 27.8