Long-Term Debt, Finance Leases, and Other Borrowings - Schedule of Long-term Debt (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Sep. 30, 2021
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	$ 678,586	$ 670,335
Less unamortized debt issuance costs	(11,083)	(9,295)
Less notes payable warrants	(9,035)	(9,630)
Net long-term debt, including current maturities	658,468	651,410
Less current portion, net of unamortized debt issuance costs	(111,059)	(111,710)
Net long-term debt	547,409	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	83,409	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	152,100	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	118,840	122,762
Other Obligations Due to Financial Institution, Collateralized by the Underlying Equipment, Due 2023 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	4,021	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	40,956	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	26,250	30,625
Notes Payable to Financial Institution Due 2023 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	3,500	4,000
Notes Payable to U.S Treasury Due 2025 [Member]
Debt Instrument [Line Items]
Gross long-term debt, including current maturities	203,069	$ 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	$ 30,811

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

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