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Revenue Recognition - Additional information (Detail) $ in Millions	3 Months Ended
	Nov. 30, 2021 USD ($)
Revenue From Contract With Customers [Line Items]
Revenue recognized from contract with customers liability	$ 9.6
Railcar sales
Revenue From Contract With Customers [Line Items]
Expected revenue recognized in the reminder of fiscal year	1,300.0
Management services
Revenue From Contract With Customers [Line Items]
Expected revenue recognized in the reminder of fiscal year	$ 128.2
Expected performance percentage	51.00%

X

- Definition

Revenue From Contract With Customers [Line Items]

+ References

No definition available.

+ Details

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Namespace Prefix:	gbx_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130549-203045

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Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130556-203045

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Balance Type:	credit
Period Type:	instant

X

- Definition

Percentage of remaining performance obligation to total remaining performance obligation not recognized as revenue.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=123351226&loc=SL49130556-203045

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- Details

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Balance Type:
Period Type:

X

- Details

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Balance Type:
Period Type: