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Nature of Operations - Additional Information (Detail)	12 Months Ended
	Aug. 31, 2021 Segment Vehicle
Number of reportable segments | Segment	3
Leasing & Services
Number of railcars owned	8,800
Number of railcars that get services	444,000

X

- Definition

Number of railcars owned.

+ References

No definition available.

+ Details

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

X

- Definition

Number of railcars with management services provided.

+ References

No definition available.

+ Details

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

X

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=123359005&loc=d3e8672-108599

+ Details

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Balance Type:	na
Period Type:	duration

X

- Details

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Namespace Prefix:
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Balance Type:
Period Type: