Debt and Other Obligations - Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Commitment fees and other	$ 2,217	$ 262
Amortization of deferred financing costs	8,714	7,069
Total	101,350	83,777
Senior loans
Debt Instrument [Line Items]
Interest expense	15,225	16,869
Junior loans
Debt Instrument [Line Items]
Interest expense	1,811	2,475
Fixed-rate term loans
Debt Instrument [Line Items]
Interest expense	25,828	19,615
2015-1 EETC Class A
Debt Instrument [Line Items]
Interest expense	14,894	16,138
2015-1 EETC Class B
Debt Instrument [Line Items]
Interest expense	3,377	3,781
2015-1 EETC Class C
Debt Instrument [Line Items]
Interest expense	5,117	3,575
2017-1 EETC Class AA
Debt Instrument [Line Items]
Interest expense	7,887	6,026
2017-1 EETC Class A
Debt Instrument [Line Items]
Interest expense	2,843	2,172
2017-1 EETC Class B
Debt Instrument [Line Items]
Interest expense	2,870	2,420
2017-1 EETC Class C
Debt Instrument [Line Items]
Interest expense	4,367	2,478
Revolving Credit Facility
Debt Instrument [Line Items]
Interest expense	5,792	793
Capital Lease Obligations
Debt Instrument [Line Items]
Interest expense	$ 408	$ 104