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Long-Term Debt and Other Borrowings - Additional Information (Detail) $ in Thousands			1 Months Ended	3 Months Ended	9 Months Ended
	Jun. 28, 2018 USD ($) Aircraft	Jun. 27, 2018 USD ($) Aircraft	Jun. 30, 2018 USD ($) Aircraft	Jun. 30, 2018 USD ($) Aircraft	Jun. 30, 2018 USD ($) Aircraft	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)
Debt Instrument [Line Items]
Property and equipment, net			$ 1,239,548	$ 1,239,548	$ 1,239,548		$ 1,192,448
Long-Term Debt			$ 994,102	994,102	994,102		$ 956,918
Non-cash lease termination expense				$ 15,109	$ 15,109
CRJ-900 [Member]
Debt Instrument [Line Items]
Refinanced debt		$ 16,000
Number of aircraft under refinanced debt | Aircraft		6	9	9	9
Refinanced debt due period		2019
Debt instrument, face amount	$ 69,600	$ 27,500	$ 27,500	$ 27,500	$ 27,500	$ 74,900
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 | Aircraft	9
Payment for aircraft purchased	$ 76,500
Non-cash lease termination expense	15,100
Future goods and services credits	4,500
Loan forgiveness for loans	$ 5,600
Equipment Notes [Member]
Debt Instrument [Line Items]
Long-Term Debt			217,900	217,900	$ 217,900
Senior Notes Due 2020 [Member] | CRJ-900 [Member]
Debt Instrument [Line Items]
Debt instrument, face amount			$ 67,300	67,300	67,300
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			$ 1,170,400	$ 1,170,400	$ 1,170,400

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