Debt and Other Obligations - Schedule of Long-term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term debt	$ 2,340.0	$ 2,213.6
Current maturities of long-term debt	334.4	214.0
Less unamortized discounts, net	41.3	40.4
Long-term debt and capital leases, less current maturities	1,964.4	1,959.2
Fixed-rate senior term loans
Debt Instrument [Line Items]
Long-term debt	$ 287.8	$ 296.1
Weighted-average interest rate	3.55%	4.02%
Fixed-rate term loans
Debt Instrument [Line Items]
Long-term debt	$ 927.4	$ 778.2
Weighted-average interest rate	3.47%	3.70%
2015-1 EETC Class A
Debt Instrument [Line Items]
Long-term debt	$ 348.6	$ 348.6
Weighted-average interest rate	4.10%	4.10%
2015-1 EETC Class B
Debt Instrument [Line Items]
Long-term debt	$ 72.0	$ 72.0
Weighted-average interest rate	4.45%	4.45%
2015-1 EETC Class C
Debt Instrument [Line Items]
Long-term debt	$ 98.1	$ 98.1
Weighted-average interest rate	4.93%	4.93%
2017-1 EETC Class AA
Debt Instrument [Line Items]
Long-term debt	$ 221.4	$ 228.4
Weighted-average interest rate	3.38%	3.38%
2017-1 EETC Class A
Debt Instrument [Line Items]
Long-term debt	$ 73.8	$ 76.1
Weighted-average interest rate	3.65%	3.65%
2017-1 EETC Class B
Debt Instrument [Line Items]
Long-term debt	$ 65.6	$ 70.6
Weighted-average interest rate	3.80%	3.80%
2017-1 EETC Class C
Debt Instrument [Line Items]
Long-term debt	$ 85.3	$ 85.5
Weighted-average interest rate	5.11%	5.11%
Revolving credit facility due in 2020
Debt Instrument [Line Items]
Long-term debt	$ 160.0	$ 160.0
Weighted-average interest rate	2.26%	3.12%
Revolving credit facility due in 2022
Debt Instrument [Line Items]
Long-term debt	$ 0.0

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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