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Long-Term Debt and Other Borrowings - Additional Information (Detail) $ in Thousands				1 Months Ended	12 Months Ended
	Aug. 14, 2018 USD ($)	Jun. 28, 2018 USD ($) Air-craft shares	Jun. 27, 2018 USD ($) Air-craft	Jun. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Debt Instrument [Line Items]
Property and equipment, net					$ 1,250,829	$ 1,192,448
Long-Term Debt					930,207	$ 956,918
Non-cash lease termination expense					$ 15,109
Warrants to purchase shares of common stock | shares		250,000
CIT revolving credit facility outstanding	$ 25,700
CRJ-900 [Member]
Debt Instrument [Line Items]
Refinanced debt			$ 16,000
Number of aircraft under refinanced debt | Air-craft		6	6
Refinanced debt due period			2019
Debt instrument, face amount		$ 69,600	$ 27,500
Net cash proceeds after transaction related fees			$ 10,400
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 purchased | Air-craft		9
Payment for aircraft purchased		$ 76,500
Number of aircraft financed | Air-craft		6	6
Non-cash lease termination expense		$ 15,100
Future goods and services credits		4,500
Loan forgiveness for loans		$ 5,600
Warrants to purchase shares of common stock | shares		250,000
Equipment Notes [Member]
Debt Instrument [Line Items]
Long-Term Debt					$ 209,200
Senior Notes Due 2020 [Member] | CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount				$ 65,800
Long term debt, basis spread on variable rate		3.50%		3.50%
Subordinated Notes Due 2020 [Member] | CRJ-900 [Member]
Debt Instrument [Line Items]
Long term debt, basis spread on variable rate		7.50%		7.50%
Aircraft and Equipment [Member] | Pledged as Collateral [Member]
Debt Instrument [Line Items]
Property and equipment, net					$ 1,047,600

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