Debt and Other Obligations (Tables)
 3 Months Ended
Mar. 31, 2021
Debt Disclosure [Abstract]  
Schedule of long-term debt
Long-term debt is comprised of the following:
As ofAs of
March 31, 2021December 31, 2020March 31, 2021December 31, 2020
(in millions)(weighted-average interest rates)
8.00% senior secured notes due in 2025
$850.0 $850.0 8.00 %8.00 %
Fixed-rate loans due through 20321,272.9 1,301.9 3.36 %3.36 %
Unsecured term loans due in 203198.7 73.3 1.00 %1.00 %
Fixed-rate class A 2015-1 EETC due through 2028322.6 322.6 4.10 %4.10 %
Fixed-rate class B 2015-1 EETC due through 202464.0 64.0 4.45 %4.45 %
Fixed-rate class C 2015-1 EETC due through 202386.6 86.6 4.93 %4.93 %
Fixed-rate class AA 2017-1 EETC due through 2030
207.3 214.4 3.38 %3.38 %
Fixed-rate class A 2017-1 EETC due through 2030
69.1 71.5 3.65 %3.65 %
Fixed-rate class B 2017-1 EETC due through 2026
58.2 60.6 3.80 %3.80 %
Fixed-rate class C 2017-1 EETC due through 2023
85.5 85.5 5.11 %5.11 %
Convertible debt due in 2025175.0 175.0 4.75 %4.75 %
Revolving credit facility due in 2021— 95.1 N/A1.55 %
Revolving credit facility due in 2024180.0 180.0 2.11 %2.15 %
Long-term debt$3,469.9 $3,580.5 
Less current maturities356.0 383.5 
Less unamortized discounts, net

66.5 131.4 
Total$3,047.4 $3,065.6 
Schedule of maturities of long-term debt
At March 31, 2021, long-term debt principal payments for the next five years and thereafter are as follows:
March 31, 2021
(in millions)
remainder of 2021$154.0 
2022192.0 
2023335.5 
2024401.0 
20251,212.2 
2026 and beyond1,175.2 
Total debt principal payments$3,469.9 
Schedule of interest expense, long-term debt
Interest expense related to long-term debt and finance leases consists of the following:
 Three Months Ended March 31,
20212020
(in thousands)
8.00% senior secured notes (1)
$17,434 $— 
Fixed-rate term loans10,903 10,426 
Unsecured term loans199 — 
Class A 2015-1 EETC3,275 3,549 
Class B 2015-1 EETC705 795 
Class C 2015-1 EETC1,056 1,209 
Class AA 2017-1 EETC1,755 1,887 
Class A 2017-1 EETC633 680 
Class B 2017-1 EETC557 644 
Class C 2017-1 EETC1,080 1,092 
Convertible debt2,078 — 
Revolving credit facilities1,170 1,159 
Finance leases24 113 
Commitment and other fees428 218 
Amortization of deferred financing costs3,509 2,106 
Total$44,806 $23,878 

(1) Includes $0.4 million of accretion and $17.0 million of interest expense for the three months ended March 31, 2021.