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Nature of Operations - Additional Information (Detail) | 12 Months Ended
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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

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- 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

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- Definition Number of railcars with management services provided. + References No definition available. + Details
Name: | gbx_NumberOfRailcarsWithManagementServicesProvided
Namespace Prefix: | gbx_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- 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
Name: | us-gaap_NumberOfReportableSegments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |