Debt and Other Obligations - Interest Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Amortization of deferred financing costs	$ 2,704	$ 2,175	$ 7,336	$ 6,544
Commitment and other fees	110	281	555	400
Total	33,435	25,138	85,105	75,375
Accretion of convertible debt and 8.00% senior secured notes			5,898	0
8.00% senior secured notes due in 2025
Debt Instrument [Line Items]
Interest expense	2,518	0	2,518	0
Accretion of convertible debt and 8.00% senior secured notes	100		100
Interest expense	2,500		2,500
Fixed-rate senior term loans
Debt Instrument [Line Items]
Interest expense	2,545	3,809	7,959	11,632
Fixed-rate junior term loans
Debt Instrument [Line Items]
Interest expense	0	454	0	1,467
Fixed-rate term loans
Debt Instrument [Line Items]
Interest expense	8,516	6,517	24,339	19,151
Unsecured term loans
Debt Instrument [Line Items]
Interest expense	169	0	226	0
2015-1 EETC Class A
Debt Instrument [Line Items]
Interest expense	3,438	3,747	10,390	11,294
2015-1 EETC Class B
Debt Instrument [Line Items]
Interest expense	760	850	2,308	2,570
2015-1 EETC Class C
Debt Instrument [Line Items]
Interest expense	1,138	1,279	3,485	3,894
2017-1 EETC Class AA
Debt Instrument [Line Items]
Interest expense	1,849	1,973	5,604	5,959
2017-1 EETC Class A
Debt Instrument [Line Items]
Interest expense	666	711	2,020	2,148
2017-1 EETC Class B
Debt Instrument [Line Items]
Interest expense	603	708	1,870	2,199
2017-1 EETC Class C
Debt Instrument [Line Items]
Interest expense	1,104	1,104	3,288	3,275
Convertible debt
Debt Instrument [Line Items]
Interest expense	5,883	0	9,021	0
Accretion of convertible debt and 8.00% senior secured notes	3,800		5,800
Interest expense	2,100		3,200
Revolving credit facilities
Debt Instrument [Line Items]
Interest expense	1,403	1,493	4,017	4,466
Finance leases
Debt Instrument [Line Items]
Interest expense	$ 29	$ 37	$ 169	$ 376