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Equity - Summary of Restricted Stock Share and Restricted Stock Unit Grant Transactions for Shares, both Vested and Unvested (Detail) - shares		12 Months Ended
		Aug. 31, 2022	Aug. 31, 2021	Aug. 31, 2020
Equity [Abstract]
Beginning Balance	[1]	5,307,000	4,959,000	4,575,000
Granted		391,000	538,000	470,000
Forfeited		(167,000)	(190,000)	(86,000)
Ending Balance	[1]	5,531,000	5,307,000	4,959,000
[1] Balance represents cumulative grants net of forfeitures.

X

- Definition

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested and Unvested, Number

+ References

No definition available.

+ Details

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Namespace Prefix:	gbx_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

X

- References

No definition available.

+ Details

Name:	us-gaap_EquityAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(03)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

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Period Type:	duration

X

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(01)
-URI https://asc.fasb.org/extlink&oid=128089324&loc=d3e5070-113901

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Balance Type:	na
Period Type:	duration