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Long-Term Debt, Finance Leases, and Other Borrowings - Schedule of Long-term Debt (Parenthetical) (Detail) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2024 | Sep. 30, 2023
Revolving Credit Facility Quaterly Collateralized By Underlying Equipment And Investments Through Two Thousand Twenty Eight [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument maturity year | 2028 | 2028
Long term debt interest rate description | quarterly interest based on SOFR plus interest spread at 4.50 |
Revolving Credit Facility Quaterly Collateralized By Underlying Equipment And Investments Through Two Thousand Twenty Eight [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] |  |
Debt Instrument [Line Items] |  |
Long term debt, basis spread on variable rate | 4.50% |
Incentive recieved | $ 10.5 |
Revolving Credit Facility Quaterly Collateralized By Underlying Equipment And Investments Through Two Thousand Twenty Eight [Member] | Maximum [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] |  |
Debt Instrument [Line Items] |  |
Incentive recieved | $ 15.0 |
Senior and Subordinated Notes Payable to Secured Parties, Due in Monthly Installments Collateralized by the Underlying Aircraft Through 2027 [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument maturity year | 2027 | 2027
Long term debt interest rate description | due in monthly installments, interest based on SOFR plus interest spread at 2.71% |
Senior and Subordinated Notes Payable to Secured Parties, Due in Monthly Installments Collateralized by the Underlying Aircraft Through 2027 [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] |  |
Debt Instrument [Line Items] |  |
Long term debt, basis spread on variable rate | 2.71% |
Notes Payable to Secured Parties, Due in Semi Annual Installments Collateralized by the Underlying Aircraft Through 2028 [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument maturity year | 2028 | 2028
Long term debt interest rate description | due in semi-annual installments, interest based on SOFR plus interest spread at 4.75% to 6.25% |
Notes Payable to Secured Parties, Due in Semi Annual Installments Collateralized by the Underlying Aircraft Through 2028 [Member] | Minimum [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] |  |
Debt Instrument [Line Items] |  |
Long term debt, basis spread on variable rate | 4.75% |
Notes Payable to Secured Parties, Due in Semi Annual Installments Collateralized by the Underlying Aircraft Through 2028 [Member] | Maximum [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] |  |
Debt Instrument [Line Items] |  |
Long term debt, basis spread on variable rate | 6.25% |
Notes Payable to Secured Parties, Due in Quarterly Installments Collateralized by the Underlying Aircraft Through 2028 [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument maturity year | 2028 | 2028
Long term debt interest rate description | due in quarterly installments, interest based on SOFR plus interest at spread 2.20% to 2.32% for senior note & 4.50% for subordinated note |
Notes Payable to Secured Parties, Due in Quarterly Installments Collateralized by the Underlying Aircraft Through 2028 [Member] | Senior Subordinated Notes [Member] |  |
Debt Instrument [Line Items] |  |
Long term debt, basis spread on variable rate | 4.50% |
Notes Payable to Secured Parties, Due in Quarterly Installments Collateralized by the Underlying Aircraft Through 2028 [Member] | Minimum [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] | Senior Notes [Member] |  |
Debt Instrument [Line Items] |  |
Long term debt, basis spread on variable rate | 2.20% |
Notes Payable to Secured Parties, Due in Quarterly Installments Collateralized by the Underlying Aircraft Through 2028 [Member] | Maximum [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] | Senior Notes [Member] |  |
Debt Instrument [Line Items] |  |
Long term debt, basis spread on variable rate | 2.32% |
Notes Payable to Financial Institution, Due in Monthly Installments Collateralized by the Underlying Equipment, Through 2024 [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument maturity year | 2024 | 2024
Long term debt interest rate description | due in monthly installments, interest based on fixed interest of 7.50%, through 2024 |
Long term debt, basis spread on variable rate | 7.50% |
Other Obligations Due to Financial Institutions, Monthly or Quarterly Collateralized by the Underlying Equipment, Due 2022 Through 2031 [Member] |  |
Debt Instrument [Line Items] |  |
Long term debt interest rate description | monthly and/or quarterly interest due from 2022 through 2031 |
Other Obligations Due to Financial Institutions, Monthly or Quarterly Collateralized by the Underlying Equipment, Due 2022 Through 2031 [Member] | Minimum [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument maturity year | 2022 | 2022
Other Obligations Due to Financial Institutions, Monthly or Quarterly Collateralized by the Underlying Equipment, Due 2022 Through 2031 [Member] | Maximum [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument maturity year | 2031 | 2031
Notes Payable to Financial Institution, Quarterly, Through 2027 [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument maturity year | 2027 | 2027
Long term debt interest rate description | Notes payable to financial institution, quarterly interest based on SOFR plus interest spread at 3.50% |
Notes Payable to Financial Institution, Quarterly, Through 2027 [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] |  |
Debt Instrument [Line Items] |  |
Long term debt, basis spread on variable rate | 3.50% |
Notes Payable To Financial Institution Due In Monthly Installments Collateralized By Underlying Equipment Through Two Thousand Twenty Four [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument maturity year | 2024 | 2024
Long term debt interest rate description | due in monthly installments, interest based on SOFR plus interest spread at 3.10% |
Notes Payable To Financial Institution Due In Monthly Installments Collateralized By Underlying Equipment Through Two Thousand Twenty Four [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] |  |
Debt Instrument [Line Items] |  |
Long term debt, basis spread on variable rate | 3.10% |
United Bridge Loan Quaterly Collateralized By Underlying Equipment And Investments Through Two Thousand Twenty Four [Member] |  |
Debt Instrument [Line Items] |  |
Long term debt interest rate description | due in quarterly installments based on SOFR plus interest spread at 4.50% |
United Bridge Loan Quaterly Collateralized By Underlying Equipment And Investments Through Two Thousand Twenty Four [Member] | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member] |  |
Debt Instrument [Line Items] |  |
Debt instrument maturity year | 2024 | 2024
Long term debt, basis spread on variable rate | 4.50% |

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