Contract Revenue and Pass-through and Other Revenue - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022
Disaggregation Of Revenue [Line Items]
Deferred Revenue	$ 9.6
Deferred revenue recognized	11.4	$ 3.0
Lease revenue	$ 123.0	$ 144.7	$ 158.4
Operating Lease, Lease Income, Statement of Income or Comprehensive Income [Extensible Enumeration]	Contract revenue	Contract revenue	Contract revenue
CRJ-700
Disaggregation Of Revenue [Line Items]
Operating lease, term of contract	9 years

Amount of deferred income and obligation to transfer product and service to customer for which consideration has been received or is receivable.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Indicates line item in statement of income or comprehensive income that includes operating lease income.

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Amount of operating lease income from lease payments and variable lease payments paid and payable to lessor. Includes, but is not limited to, variable lease payments not included in measurement of lease receivable.

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