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Long-Term Debt, Finance Leases, and Other Borrowings - Additional Information (Detail)									1 Months Ended	3 Months Ended		12 Months Ended
	Nov. 13, 2020 USD ($)	Nov. 12, 2020 USD ($) Air-craft	Oct. 30, 2020 USD ($) $ / shares shares	Oct. 01, 2020 USD ($)	Sep. 27, 2019 USD ($)	Sep. 25, 2019 USD ($)	Jun. 14, 2019 USD ($) Air-craft	Jan. 28, 2019 USD ($)	Jun. 30, 2019 USD ($) Airfleet	Dec. 31, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2021 USD ($) $ / shares	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Nov. 14, 2020 USD ($)	Apr. 09, 2020 $ / shares	Jun. 28, 2018 shares
Debt Instrument [Line Items]
Property and equipment, net												$ 1,151,891,000	$ 1,212,415,000
Long-Term Debt												651,410,000	731,724,000
Loss (gain) on extinguishment of debt												(950,000)		$ 3,616,000
Payment for debt extinguishment prepayment penalties														1,672,000
Non-cash lease termination expense												4,508,000		9,540,000
Proceeds from long-term debt												195,000,000	23,000,000	$ 171,658,000
Debt outstanding												$ 670,335,000	743,250,000
Warrants to purchase shares of common stock \| shares																	250,000
Warrants of common stock exercise price \| $ / shares												$ 0.004				$ 3.98
Treasury Loan [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Calculated collateral coverage ratio			1.6
Treasury Loan [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Additional collateral coverage ratio			1.6
Loan Agreement [Member]
Debt Instrument [Line Items]
Repayments of long term debt		$ 167,700,000
Secured term loan facility, amount borrowed			$ 43,000,000.0
Secured term loan facility, additional amount borrowed	$ 152,000,000.0
Warrants to purchase shares of common stock \| shares			4,899,497
Warrants of common stock exercise price \| $ / shares			$ 3.98
Debt issuance costs allocated to warrants												$ 100,000
Number of aircraft financed \| Air-craft		44
Loan Agreement [Member] \| EDC Loans [Member]
Debt Instrument [Line Items]
Repayments of long term debt	1,000,000.0
Debt issuance costs	3,100,000
Payment of loans		$ 164,200,000
Discount for balance amount of loans		$ 3,500,000
Debt discount	2,500,000
Loan Agreement [Member] \| FortyThreeMillionTreasuryLoanMember
Debt Instrument [Line Items]
Capitalized debt issuance costs, net			$ 700,000
Loan Agreement [Member] \| $152M Treasury Loan [Member]
Debt Instrument [Line Items]
Capitalized debt issuance costs, net	2,300,000
Export Development Canada [Member]
Debt Instrument [Line Items]
Principal payments deferred													28,000,000.0
Repayments of long term debt										$ 167,700,000
Repayments of previously deferred principal payments				$ 19,900,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Proceeds from long-term debt													23,000,000.0
Debt outstanding												22,930,000	22,930,000
Equipment Notes [Member]
Debt Instrument [Line Items]
Long-Term Debt												$ 152,100,000
Term Loan [Member]
Debt Instrument [Line Items]
Debt instrument, face amount								$ 91,200,000
Long term debt interest rate description												LIBOR plus 3.10%
Term loan, term								5 years
Write-off of financing cost								$ 1,900,000
Payment for debt extinguishment prepayment penalties								1,700,000
Term Loan [Member] \| Spare Engine Facility [Member]
Debt Instrument [Line Items]
Long term debt interest rate description												LIBOR plus 7.25%
Loss (gain) on extinguishment of debt								$ 3,600,000
Term Loan [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate								3.10%
Term Loan [Member] \| LIBOR [Member] \| Spare Engine Facility [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate								7.25%
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2023 [Member]
Debt Instrument [Line Items]
Debt outstanding												$ 30,625,000	48,125,000
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2023 [Member] \| CRJ-700 Aircraft [Member]
Debt Instrument [Line Items]
Debt instrument, face amount							$ 70,000,000.0		$ 70,000,000.0
Long term debt interest rate description												LIBOR plus 5.00%
Number of aircraft purchased \| Air-craft							10
Payment for aircraft purchased							$ 70,000,000.0
Non-cash lease termination expense							$ 9,500,000
Number of aircraft financed \| Airfleet									10
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2023 [Member] \| LIBOR [Member] \| CRJ-700 Aircraft [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate							5.00%		5.00%
Working Capital Draw Loan [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, face amount						$ 35,000,000.0
Long term debt interest rate description												one-month LIBOR plus 3.75%.
Term loan, term						3 years
Proceeds from long-term debt											$ 23,000,000.0		23,000,000.0
Debt outstanding												$ 22,900,000
Working Capital Draw Loan [Member] \| LIBOR [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate						3.75%
Notes Payable to Financial Institution Due 2023 [Member]
Debt Instrument [Line Items]
Debt outstanding												$ 4,000,000	$ 6,000,000
Secured Term Loan Facility [Member] \| Loan Agreement [Member]
Debt Instrument [Line Items]
Long term debt interest rate description												three-month LIBOR plus 3.50%
Long term debt, basis spread on variable rate			3.50%
Secured term loan facility, maximum borrowing capacity			$ 200,000,000.0
Secured term loan facility, amount borrowed			$ 43,000,000.0
Secured term loan facility, additional amount borrowed	152,000,000.0														$ 0
Debt instrument, maturity date												Oct. 30, 2025
Secured Term Loan Facility [Member] \| Loan Agreement [Member] \| Treasury Loan [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate			3.50%
Secured term loan facility, amount borrowed			$ 43,000,000.0
Secured term loan facility, additional amount borrowed	$ 152,000,000.0														$ 0
Debt instrument, maturity date			Oct. 30, 2025
Aircraft and Equipment [Member] \| Pledged as Collateral [Member]
Debt Instrument [Line Items]
Property and equipment, net												$ 1,027,900,000
Flight Equipment [Member] \| Notes Payable to Financial Institution Due 2023 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount					$ 8,000,000.0
Long term debt interest rate description												monthly LIBOR plus 5.00%		Libor plus 5.0%.
Flight Equipment [Member] \| Notes Payable to Financial Institution Due 2023 [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate					5.00%