Fair Value Measurements - Long-term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2022	Nov. 17, 2022	Dec. 31, 2021	Sep. 17, 2020	May 12, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 3,642.4		$ 3,238.2
Estimated Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	$ 3,355.0		$ 3,275.8
Secured Debt | 8.00% senior secured notes due in 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate percentage	8.00%	8.00%	8.00%	8.00%
Carrying Value	$ 1,110.0		$ 510.0
Secured Debt | Estimated Fair Value | Level 3 | 8.00% senior secured notes due in 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	1,085.0		530.4
Fixed-rate term loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	1,094.7		1,223.5
Fixed-rate term loans | Estimated Fair Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	1,003.9		1,262.6
Unsecured term loans due through 2031 | Unsecured term loans due through 2031
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	136.3		136.3
Unsecured term loans due through 2031 | Estimated Fair Value | Level 3 | Unsecured term loans due through 2031
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	116.0		146.4
2015-1 EETC Class A
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	278.6		300.6
2015-1 EETC Class A | Estimated Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	247.5		311.1
2015-1 EETC Class B
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	48.0		56.0
2015-1 EETC Class B | Estimated Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	45.6		56.4
2015-1 EETC Class C
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	63.8		75.2
2015-1 EETC Class C | Estimated Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	63.1		74.0
2017-1 EETC Class AA
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	186.3		200.3
2017-1 EETC Class AA | Estimated Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	161.6		203.3
2017-1 EETC Class A
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	62.1		66.8
2017-1 EETC Class A | Estimated Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	52.3		65.8
2017-1 EETC Class B
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	51.7		55.8
2017-1 EETC Class B | Estimated Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	44.9		53.6
2017-1 EETC Class C
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	85.5		85.5
2017-1 EETC Class C | Estimated Fair Value | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	$ 85.1		84.1
Convertible notes | Convertible notes due in 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate percentage	4.75%				4.75%
Carrying Value	$ 25.4		28.2
Convertible notes | Convertible notes due in 2026
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Stated interest rate percentage	1.00%
Carrying Value	$ 500.0		500.0
Convertible notes | Estimated Fair Value | Level 2 | Convertible notes due in 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	44.9		55.6
Convertible notes | Estimated Fair Value | Level 2 | Convertible notes due in 2026
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated Fair Value	$ 405.1		$ 432.5