Long-Term Debt, Financing Leases and Other Borrowings - Schedule of Long-term Debt (Parenthetical) (Detail) $ in Thousands				1 Months Ended					3 Months Ended		6 Months Ended		12 Months Ended
	Sep. 27, 2019 USD ($)	Sep. 25, 2019 USD ($)	Jun. 14, 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	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($) 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	$ 91,200
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									3.24%		3.24%
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											LIBOR plus a spread ranging from 1.95% to 7.25%
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] \| Minimum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage									2.94%		2.94%								1.95%
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] \| Ten C- R- J-900 Aircraft [Member] \| LIBOR [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage									8.24%		8.24%								7.25%
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%		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%		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%
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
Debt instrument, face amount													$ 26,100	$ 26,100	$ 26,100	$ 26,100
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									4.38%		4.38%
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									4.66%		4.66%
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									4.52%		4.52%
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									4.09%		4.09%
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 Aircraft [Member]
Debt Instrument [Line Items]
Debt instrument, face amount			$ 70,000	$ 70,000
Long term debt interest rate percentage									5.99%		5.99%
Long term debt interest rate description			LIBOR plus 5.0%								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 Aircraft [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt basis spread on variable rate				5.25%						5.00%	5.00%		5.25%
Notes Payable to Financial Institution Due 2023 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year											2023		2023
Notes Payable to Financial Institution Due 2023 [Member] \| Flight Equipment [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 8,000
Long term debt interest rate percentage									5.99%		5.99%
Long term debt interest rate description	Libor plus 5.0%.										monthly LIBOR plus 5.00%
Notes Payable to Financial Institution Due 2023 [Member] \| Flight Equipment [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt basis spread on variable rate	5.25%									5.00%	5.00%		5.25%
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									3.70%		3.70%
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									3.65%		3.65%
Senior Notes Due 2008 [Member] \| Eight E-175 Aircraft [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage									3.77%		3.77%
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%		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									4.95%		4.95%
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									8.95%		8.95%
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									4.95%		4.95%
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									5.95%		5.95%
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%
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 5.24%
Term loan, term		3 years
Debt instrument, expiration year and month		2022-09
Proceeds from long-term debt									$ 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		5.24%