Debt and Other Obligations - Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Commitment fees	$ 262	$ 124
Amortization of deferred financing costs	7,069	5,280
Total	83,777	57,302
Equipment Notes, Series C 2017-1
Debt Instrument [Line Items]
Interest expense, debt	2,478	0
2017-1 EETC Class B
Debt Instrument [Line Items]
Interest expense, debt	2,420	22
2017-1 EETC Class A
Debt Instrument [Line Items]
Interest expense, debt	2,172	19
Equipment Notes, Series C 2015-1
Debt Instrument [Line Items]
Interest expense, debt	3,575	0
2017-1 EETC Class AA
Debt Instrument [Line Items]
Interest expense, debt	6,026	54
2015-1 EETC Class B
Debt Instrument [Line Items]
Interest expense, debt	3,781	4,446
2015-1 EETC Class A
Debt Instrument [Line Items]
Interest expense, debt	16,138	17,230
Fixed-rate term loans
Debt Instrument [Line Items]
Interest expense, debt	19,615	8,610
Junior loans
Debt Instrument [Line Items]
Interest expense, debt	2,475	3,035
Senior loans
Debt Instrument [Line Items]
Interest expense, debt	16,869	18,328
Revolving Credit Facility
Debt Instrument [Line Items]
Interest expense, debt	793	0
Capital Lease Obligations
Debt Instrument [Line Items]
Interest expense, debt	$ 104	$ 154

Amount of amortization expense attributable to debt discount (premium) and debt issuance costs.

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