Long-Term Debt and Other Borrowings - Schedule of Long-term Debt (Parenthetical) (Detail) $ in Thousands			1 Months Ended					3 Months Ended		12 Months Ended
	Sep. 27, 2019 USD ($)	Sep. 25, 2019 USD ($)	Jun. 30, 2019 USD ($) Airfleet	Jan. 31, 2019 USD ($)	Jun. 30, 2018 USD ($) Air-craft	Feb. 28, 2018 Engine	Dec. 31, 2017 USD ($) Air-craft	Mar. 31, 2020 USD ($)	Dec. 31, 2019	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017	Sep. 30, 2016 USD ($) Air-craft	Sep. 30, 2015 USD ($) Air-craft	Sep. 30, 2007 USD ($) Airfleet	Sep. 30, 2014 USD ($) Airfleet
Debt Instrument [Line Items]
Proceeds from long-term debt										$ 23,000	$ 171,658	$ 187,703
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Proceeds from long-term debt										$ 23,000
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year										2022	2022
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Number of aircraft refinanced \| Airfleet																3
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] \| CRJ-700 [Member]
Debt Instrument [Line Items]
Number of aircraft refinanced \| Airfleet																3
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] \| Three C- R- J-900 and Three C- R- J-700 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount																$ 120,300
Long term debt interest rate percentage										2.40%
Long term debt interest rate description										monthly LIBOR plus 2.25%
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] \| Three C- R- J-900 and Three C- R- J-700 [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate																2.25%
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] \| Ten C- R- J-900 Aircraft [Member]
Debt Instrument [Line Items]
Debt instrument, face amount																	$ 88,400
Long term debt interest rate description										monthly LIBOR plus 1.95%
Number of aircraft financed \| Airfleet																	10
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] \| Ten C- R- J-900 Aircraft [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage										2.10%							1.95%
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] \| Four C- R- J-900 Aircraft [Member]
Debt Instrument [Line Items]
Repayments of long term debt												$ 40,000
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2024 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year										2024	2024
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2024 [Member] \| Eight C- R- J-900 Aircraft [Member]
Debt Instrument [Line Items]
Debt instrument, face amount																	$ 114,500
Number of aircraft financed \| Airfleet																	8
Long term debt interest rate percentage																	5.00%
Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2027 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year										2027	2027
Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2027 [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount															$ 170,200
Number of aircraft financed \| Air-craft															7
Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year										2028	2028
Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member] \| Ten E-175 Aircraft [Member]
Debt Instrument [Line Items]
Debt instrument, face amount														$ 246,000
Number of aircraft financed \| Air-craft														10
Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member] \| Ten E-175 Aircraft [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage										4.75%
Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member] \| Ten E-175 Aircraft [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage										6.25%
Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year										2028	2028
Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2028 [Member] \| Eight E-175 Aircraft [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Number of aircraft refinanced \| Air-craft														8
Debt instrument, face amount														$ 195,300
Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year										2022	2022
Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2022 [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year										2022	2022
Number of aircraft refinanced \| Air-craft					6		9
Debt instrument, face amount					$ 27,500		$ 74,900
Number of aircraft financed \| Air-craft					9
Senior and Subordinated Notes Payable to Secured Parties, Collateralized by the Underlying Aircraft, Due 2022 [Member] \| CRJ-900 [Member] \| Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Debt instrument, face amount					$ 69,600
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] \| Flight Equipment [Member]
Debt Instrument [Line Items]
Debt instrument maturity year										2020	2020
Debt instrument, face amount															$ 8,300
Long term debt interest rate percentage															5.163%
Debt instrument, repayment date															2020-08
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] \| Flight Equipment Maintenance [Member]
Debt Instrument [Line Items]
Debt instrument maturity year										2020	2020
Long term debt interest rate description										three-month LIBOR plus a spread ranging from 2.93% to 3.21%
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] \| Flight Equipment Maintenance [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage										3.16%
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] \| Flight Equipment Maintenance [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage										3.44%
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] \| Flight Equipment Maintenance [Member] \| LIBOR [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate											2.93%	2.93%	2.93%	2.93%
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] \| Flight Equipment Maintenance [Member] \| LIBOR [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate											3.21%	3.21%	3.21%	3.21%
Notes Payable to Financial Institution Due 2020 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year										2020	2020
Notes Payable to Financial Institution Due 2020 [Member] \| Flight Equipment Maintenance [Member]
Debt Instrument [Line Items]
Debt instrument, face amount														$ 10,200	$ 10,200
Long term debt interest rate percentage										3.30%
Long term debt interest rate description										three-month LIBOR plus 3.07%
Notes Payable to Financial Institution Due 2020 [Member] \| Flight Equipment Maintenance [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage														3.07%	3.07%
Other Obligations Due to Financial Institution, Collateralized by the Underlying Equipment, Due 2023 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year										2023	2023
Imputed interest						9.128%
Number of spare engines leased \| Engine						2
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2024 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year										2024	2024
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2024 [Member] \| Flight Equipment [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				$ 91,200
Long term debt interest rate percentage										3.25%
Long term debt interest rate description										monthly LIBOR plus 3.10%
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2024 [Member] \| Flight Equipment [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate				3.10%
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2023 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year										2023	2023
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2023 [Member] \| CRJ-700 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount			$ 70,000
Long term debt interest rate percentage										5.15%
Long term debt interest rate description										monthly LIBOR plus 5.00%
Number of aircraft financed \| Airfleet			10
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2023 [Member] \| CRJ-700 [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate			5.00%						5.00%		5.25%
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2023 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year										2023	2023
Senior Notes Due Two Thousand Twenty Seven [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount															$ 151,000
Long term debt interest rate percentage										2.86%
Long term debt interest rate description										monthly LIBOR plus 2.71%
Senior Notes Due Two Thousand Twenty Seven [Member] \| CRJ-900 [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate															2.71%
Subordinated Notes Due Two Thousand Twenty Seven [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Imputed interest															6.25%
Debt discount															$ 8,100
Senior Notes Due 2008 [Member] \| Eight E-175 Aircraft [Member]
Debt Instrument [Line Items]
Long term debt interest rate description										three-month LIBOR plus a spread ranging from 2.20% to 2.32%
Senior Notes Due 2008 [Member] \| Eight E-175 Aircraft [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, face amount														$ 172,000
Long term debt interest rate percentage										2.43%
Senior Notes Due 2008 [Member] \| Eight E-175 Aircraft [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage										2.55%
Senior Notes Due 2008 [Member] \| Eight E-175 Aircraft [Member] \| LIBOR [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate														2.20%
Senior Notes Due 2008 [Member] \| Eight E-175 Aircraft [Member] \| LIBOR [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate														2.32%
Subordinated Notes Due 2008 [Member] \| Eight E-175 Aircraft [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage										4.50%
Senior Notes Due 2020 [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount					$ 65,800
Long term debt interest rate percentage										3.73%
Long term debt, basis spread on variable rate					3.50%
Senior Notes Due 2020 [Member] \| CRJ-900 [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt interest rate description										three-month LIBOR plus 3.50%
Subordinated Notes Due 2020 [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount					$ 29,800
Long term debt interest rate percentage										7.73%
Long term debt, basis spread on variable rate					7.50%
Subordinated Notes Due 2020 [Member] \| CRJ-900 [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt interest rate description										three month LIBOR plus 7.50%
Senior Notes due Two Thousand Twenty Two [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount							$ 46,900
Long term debt interest rate percentage										3.73%
Long term debt interest rate description										three-month LIBOR plus 3.50%
Senior Notes due Two Thousand Twenty Two [Member] \| CRJ-900 [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate							3.50%
Subordinated Notes DueTwoThousandTwentyTwo [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage										4.73%
Long term debt interest rate description										three-month LIBOR plus 4.50%
Subordinated Notes DueTwoThousandTwentyTwo [Member] \| CRJ-900 [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage							4.50%
Notes Payable to Financial Institution, Collateralized by the Underlying, Due 2023 [Member] \| Flight Equipment [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 8,000
Long term debt interest rate percentage										5.15%
Long term debt interest rate description										monthly LIBOR plus 5.00%
Notes Payable to Financial Institution, Collateralized by the Underlying, Due 2023 [Member] \| Flight Equipment [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate	5.00%								5.00%		5.25%
Working Capital Draw Loan [Member] \| Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, face amount		$ 35,000
Long term debt interest rate description										one-month LIBOR plus 3.75%.	one-month LIBOR plus 3.75%.
Term loan, term		3 years
Debt instrument, expiration year and month		2022-09
Proceeds from long-term debt								$ 23,000		$ 23,000
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%