Debt and Other Obligations - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Debt Instrument [Line Items]
Amortization of deferred financing costs	$ 2,526	$ 2,177	$ 4,632	$ 4,369
Commitment and other fees	228	46	445	119
Total	27,792	25,266	51,670	50,237
Fixed-rate senior term loans
Debt Instrument [Line Items]
Interest expense	2,601	3,878	5,414	7,823
Fixed-rate junior term loans
Debt Instrument [Line Items]
Interest expense	0	489	0	1,012
Fixed-rate term loans
Debt Instrument [Line Items]
Interest expense	8,210	6,432	15,823	12,634
Unsecured term loans
Debt Instrument [Line Items]
Interest expense	57	0	57	0
2015-1 EETC Class A
Debt Instrument [Line Items]
Interest expense	3,403	3,709	6,952	7,547
2015-1 EETC Class B
Debt Instrument [Line Items]
Interest expense	752	841	1,548	1,721
2015-1 EETC Class C
Debt Instrument [Line Items]
Interest expense	1,138	1,280	2,347	2,615
2017-1 EETC Class AA
Debt Instrument [Line Items]
Interest expense	1,868	1,997	3,755	3,986
2017-1 EETC Class A
Debt Instrument [Line Items]
Interest expense	673	720	1,354	1,437
2017-1 EETC Class B
Debt Instrument [Line Items]
Interest expense	623	737	1,267	1,491
2017-1 EETC Class C
Debt Instrument [Line Items]
Interest expense	1,092	1,092	2,184	2,171
Convertible debt
Debt Instrument [Line Items]
Interest expense	3,138	0	3,138	0
Revolving credit facilities
Debt Instrument [Line Items]
Interest expense	1,456	1,559	2,614	2,973
Finance leases
Debt Instrument [Line Items]
Interest expense	$ 27	$ 309	$ 140	$ 339