Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2024

Fair Value Disclosures [Abstract]

Carrying Amount and Estimated Fair Value, Long-term Debt

The carrying amounts and estimated fair values of the Company's long-term debt at March 31, 2024 and December 31, 2023 were as follows:

	March 31, 2024				December 31, 2023				Fair Value Level Hierarchy
	Carrying Value		Estimated Fair Value		Carrying Value		Estimated Fair Value
	(in millions)
8.00% senior secured notes	$	1,110.0	$	1,112.2	$	1,110.0	$	1,121.9	Level 3
Fixed-rate term loans	1,055.8		1,060.3		1,093.3		1,099.9		Level 3
Unsecured term loans	136.3		129.3		136.3		128.3		Level 3
2015-1 EETC Class A	256.6		233.9		256.6		230.8		Level 2
2015-1 EETC Class B	40.0		40.0		40.0		39.4		Level 2
2017-1 EETC Class AA	166.2		147.3		172.2		149.6		Level 2
2017-1 EETC Class A	55.4		47.7		57.4		48.5		Level 2
2017-1 EETC Class B	46.4		40.1		48.2		42.9		Level 2
4.75% convertible notes due 2025	25.1		19.0		25.1		42.3		Level 2
1.00% convertible notes due 2026	500.0		240.0		500.0		349.9		Level 2
Total long-term debt	$	3,391.8	$	3,069.8	$	3,439.1	$	3,253.5

Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis

Assets and liabilities measured at gross fair value on a recurring basis are summarized below:

	Fair Value Measurements as of March 31, 2024
	Total		Level 1		Level 2		Level 3
	(in millions)
Cash and cash equivalents	$	764.8	$	764.8	$	—	$	—
Restricted cash	133.6		133.6		—		—
Short-term investment securities	113.9		113.9		—		—
Total assets	$	1,012.3	$	1,012.3	$	—	$	—
Total liabilities	$	—	$	—	$	—	$	—

	Fair Value Measurements as of December 31, 2023
	Total		Level 1		Level 2		Level 3
	(in millions)
Cash and cash equivalents	$	865.2	$	865.2	$	—	$	—
Restricted cash	119.4		119.4		—		—
Short-term investment securities	112.5		112.5		—		—
Total assets	$	1,097.1	$	1,097.1	$	—	$	—
Derivative liability	$	11.1	$	—	11.1		$	—
Total liabilities	$	11.1	$	—	$	11.1	$	—