Long-Term Debt and Other Borrowings - Schedule of Long-term Debt (Parenthetical) (Detail) $ in Millions			1 Months Ended			12 Months Ended
	Jun. 28, 2018 USD ($) Air-craft	Jun. 27, 2018 USD ($) Air-craft	Jun. 30, 2018 USD ($) Air-craft	Feb. 28, 2018 Engine	Dec. 31, 2017 USD ($) Air-craft	Sep. 30, 2018	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($) Air-craft	Sep. 30, 2015 USD ($) Air-craft	Sep. 30, 2014 USD ($) Airfleet	Sep. 30, 2007 USD ($) Airfleet	Sep. 30, 2005 USD ($) Airfleet
CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 69.6	$ 27.5
Long term debt interest rate description	LIBOR plus a spread ranging from 3.50% for the senior promissory notes to 7.50% for the subordinated promissory notes					LIBOR plus 3.50%.
Long term debt basis spread on variable rate		3.50%
Number of aircraft financed \| Air-craft	6	6
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2019 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year						2019	2019
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2019 [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Number of aircraft refinanced \| Airfleet										9		5
Debt instrument, face amount												$ 118.0
Long term debt interest rate description						London InterBank Offered Rate (“LIBOR”), plus 3%
Long term debt interest rate percentage						5.261%
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2019 [Member] \| CRJ-900 [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt basis spread on variable rate												3.00%
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2019 [Member] \| CRJ-700 [Member]
Debt Instrument [Line Items]
Number of aircraft refinanced \| Airfleet										5
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2019 [Member] \| Five C- R- J-700 and Nine C- R- J-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount										$ 254.7
Long term debt interest rate description						monthly LIBOR plus 3%
Long term debt interest rate percentage						5.261%
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2019 [Member] \| Five C- R- J-700 and Nine C- R- J-900 [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt basis spread on variable rate										3.00%
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											$ 120.3
Long term debt interest rate description						monthly LIBOR plus 2.25%
Long term debt interest rate percentage						4.511%
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										$ 88.4
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] \| Minimum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage						4.211%
Notes Payable to Financial Institution, Collateralized by the Underlying Aircraft, Due 2022 [Member] \| Ten C- R- J-900 Aircraft [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage						9.511%
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						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						7.25%
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										$ 114.5
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									$ 170.2
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								$ 246.0
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								$ 195.3
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			$ 27.5		$ 74.9
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			$ 69.6
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2022 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year						2022	2022
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2022 [Member] \| Flight Equipment [Member]
Debt Instrument [Line Items]
Debt instrument, face amount							$ 99.1
Long term debt interest rate description						monthly LIBOR plus 7.25%
Long term debt interest rate percentage							9.511%
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2022 [Member] \| Flight Equipment [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt basis spread on variable rate							7.25%
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] \| Flight Equipment Maintenance [Member]
Debt Instrument [Line Items]
Debt instrument, face amount							$ 11.9	$ 11.9
Long term debt interest rate description						Three-month LIBOR plus a spread ranging from 2.93% to 2.96%
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] \| Minimum [Member] \| Flight Equipment Maintenance [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage						5.328%
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] \| Maximum [Member] \| Flight Equipment Maintenance [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage						5.358%
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] \| LIBOR [Member] \| Minimum [Member] \| Flight Equipment Maintenance [Member]
Debt Instrument [Line Items]
Long term debt basis spread on variable rate							2.93%	2.93%
Notes Payable to Financial Institution, Collateralized by the Underlying Equipment, Due 2020 [Member] \| LIBOR [Member] \| Maximum [Member] \| Flight Equipment Maintenance [Member]
Debt Instrument [Line Items]
Long term debt basis spread on variable rate							2.96%	2.96%
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									$ 8.3
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
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								$ 10.2	$ 10.2
Long term debt interest rate description						three-month LIBOR plus 3.07%
Long term debt interest rate percentage						5.468%
Notes Payable to Financial Institution Due 2020 [Member] \| LIBOR [Member] \| Flight Equipment Maintenance [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage								3.07%	3.07%
Notes Payable to Financial Institution Due 2019 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year						2019	2019
Notes Payable to Financial Institution Due 2019 [Member] \| Flight Equipment Maintenance [Member]
Debt Instrument [Line Items]
Debt instrument, face amount							$ 25.0
Long term debt interest rate description						Three-month LIBOR plus 3.30%
Long term debt basis spread on variable rate							3.30%
Notes Payable to Financial Institution Due 2019 [Member] \| Flight Equipment Maintenance [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage						5.698%
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
Senior Notes Due Two Thousand Twenty Seven [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount									$ 151.0
Long term debt interest rate description						monthly LIBOR plus 2.71%
Long term debt interest rate percentage						4.971%
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									$ 8.1
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								$ 172.0
Long term debt interest rate percentage						4.598%
Senior Notes Due 2008 [Member] \| Eight E-175 Aircraft [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage						4.718%
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 Two Thousand Twenty Two [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount					$ 46.9
Long term debt interest rate description						three-month LIBOR plus 3.50
Long term debt interest rate percentage						5.898%
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 description						three-month LIBOR plus 4.50%
Long term debt interest rate percentage						6.898%
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, Collateralized by Certain Flight Equipment and Spare Parts [Member]
Debt Instrument [Line Items]
Debt instrument, face amount								$ 35.0
Long term debt interest rate description						One-month LIBOR plus 4.25%
Long term debt basis spread on variable rate								4.25%
Working Capital Draw Loan, Collateralized by Certain Flight Equipment and Spare Parts [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage						6.511%
Senior Notes Due 2020 [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount			$ 65.8
Long term debt interest rate percentage						5.898%
Long term debt basis spread on variable rate	3.50%		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]
Long term debt interest rate percentage						9.898%
Long term debt basis spread on variable rate	7.50%		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%