Long-Term Debt and Other Borrowings - Schedule of Long-term Debt (Parenthetical) (Detail)			1 Months Ended			3 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	Dec. 31, 2018 USD ($)	Sep. 30, 2018	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($) Air-craft	Sep. 30, 2015 USD ($) Air-craft	Sep. 30, 2007 USD ($) Airfleet	Sep. 30, 2005 USD ($) Airfleet	Sep. 30, 2004 USD ($) Airfleet	Sep. 30, 2014 USD ($) Airfleet
CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount	$ 69,600,000	$ 27,500,000
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												5	9
Debt instrument, face amount												$ 118,000,000
Long term debt interest rate description						London Inter-bank Offered Rate ("LIBOR"), plus 3%
Long term debt interest rate percentage						5.503%
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
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													$ 254,700,000
Long term debt interest rate description						monthly LIBOR plus 3%
Long term debt interest rate percentage						5.503%
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
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											$ 120,300,000
Long term debt interest rate description						monthly LIBOR plus 2.25%
Long term debt interest rate percentage						4.753%
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														$ 88,400,000
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						4.453%
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						9.753%
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														$ 114,500,000
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										$ 170,200,000
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									$ 246,000,000
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									$ 195,300,000
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			$ 27,500,000		$ 74,900,000
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			$ 69,600,000
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								$ 99,100,000
Long term debt interest rate description						monthly LIBOR plus 7.25%
Long term debt interest rate percentage						9.753%
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 [Member]
Debt Instrument [Line Items]
Debt instrument maturity year						2020	2020
Debt instrument, face amount										$ 8,300,000
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								$ 11,900,000	$ 11,900,000
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] \| Flight Equipment Maintenance [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage						5.738%
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						5.768%
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%
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								2.96%	2.96%
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									$ 10,200,000	$ 10,200,000
Long term debt interest rate description						monthly LIBOR plus 3.07%
Long term debt interest rate percentage						5.878%
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%
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								$ 25,000,000
Long term debt interest rate description						Tree-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						6.108%
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										$ 151,000,000
Long term debt interest rate description						monthly LIBOR plus 2.71%
Long term debt interest rate percentage						5.213%
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										$ 8,100,000
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									$ 172,000,000
Long term debt interest rate percentage						5.008%
Senior Notes Due 2008 [Member] \| Eight E-175 Aircraft [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Long term debt interest rate percentage						5.128%
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					$ 46,900,000
Long term debt interest rate description						three-month LIBOR plus 3.50
Long term debt interest rate percentage						6.308%
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						7.308%
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									$ 35,000,000
Long term debt interest rate description						one-month LIBOR plus 4.25%
Long term debt basis spread on variable rate									4.25%
Outstanding facility borrowings						$ 0
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						6.753%
Senior Notes Due 2020 [Member] \| CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount			$ 67,300,000
Long term debt interest rate percentage						6.308%
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						10.308%
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%