Long-Term Debt, Finance Leases, and Other Borrowings - Schedule of Long-term Debt (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Sep. 30, 2021
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	$ 653,396	$ 670,335
Less unamortized debt issuance costs	(9,522)	(9,295)
Less notes payable warrants	(7,867)	(9,630)
Net long-term debt, including current maturities	636,007	651,410
Less current portion, net of unamortized debt issuance costs	(112,776)	(111,710)
Net long-term debt	523,231	539,700
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	15,630	22,930
Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2027 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	77,058	86,551
Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	141,690	152,100
Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	110,892	122,762
Other Obligations Due to Financial Institutions, Collateralized by the Underlying Equipment, Due 2023 and 2024 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	18,481	4,581
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2024 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	31,557	45,559
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2023 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	17,500	30,625
Notes Payable to Financial Institution Due 2023 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	2,500	4,000
Notes Payable to U.S Treasury Due 2025 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	204,947	$ 201,227
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2027 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	$ 33,141

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount of unamortized debt discount (premium) and debt issuance costs.

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Amount, excluding unamortized premium (discount) and debt issuance cost, of long-term debt. Excludes lease obligation.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Sum of the carrying values as of the balance sheet date of the portions of all long-term notes and loans payable due within one year or the operating cycle if longer.

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