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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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

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Fair Value Measurements - Long-term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Apr. 30, 2021	May 12, 2020
Debt Instrument [Line Items]
Carrying Value	$ 3,391.8	$ 3,439.1
Secured Debt \| 8.00% senior secured notes
Debt Instrument [Line Items]
Stated interest rate percentage	8.00%	8.00%	8.00%
Carrying Value	$ 1,110.0	$ 1,110.0
Fixed-rate term loans
Debt Instrument [Line Items]
Carrying Value	1,055.8	1,093.3
Unsecured term loans \| Unsecured term loans
Debt Instrument [Line Items]
Carrying Value	136.3	136.3
2015-1 EETC Class A
Debt Instrument [Line Items]
Carrying Value	256.6	256.6
2015-1 EETC Class B
Debt Instrument [Line Items]
Carrying Value	40.0	40.0
2017-1 EETC Class AA
Debt Instrument [Line Items]
Carrying Value	166.2	172.2
2017-1 EETC Class A
Debt Instrument [Line Items]
Carrying Value	55.4	57.4
2017-1 EETC Class B
Debt Instrument [Line Items]
Carrying Value	$ 46.4	$ 48.2
Convertible Notes \| 4.75% convertible notes due 2025
Debt Instrument [Line Items]
Stated interest rate percentage	4.75%	4.75%			4.75%
Carrying Value	$ 25.1	$ 25.1
Convertible Notes \| 1.00% convertible notes due 2026
Debt Instrument [Line Items]
Stated interest rate percentage	1.00%	1.00%		1.00%
Carrying Value	$ 500.0	$ 500.0
Estimated Fair Value
Debt Instrument [Line Items]
Estimated Fair Value	3,069.8	3,253.5
Estimated Fair Value \| Level 3 \| Secured Debt \| 8.00% senior secured notes
Debt Instrument [Line Items]
Estimated Fair Value	1,112.2	1,121.9
Estimated Fair Value \| Level 3 \| Fixed-rate term loans
Debt Instrument [Line Items]
Estimated Fair Value	1,060.3	1,099.9
Estimated Fair Value \| Level 3 \| Unsecured term loans \| Unsecured term loans
Debt Instrument [Line Items]
Estimated Fair Value	129.3	128.3
Estimated Fair Value \| Level 2 \| 2015-1 EETC Class A
Debt Instrument [Line Items]
Estimated Fair Value	233.9	230.8
Estimated Fair Value \| Level 2 \| 2015-1 EETC Class B
Debt Instrument [Line Items]
Estimated Fair Value	40.0	39.4
Estimated Fair Value \| Level 2 \| 2017-1 EETC Class AA
Debt Instrument [Line Items]
Estimated Fair Value	147.3	149.6
Estimated Fair Value \| Level 2 \| 2017-1 EETC Class A
Debt Instrument [Line Items]
Estimated Fair Value	47.7	48.5
Estimated Fair Value \| Level 2 \| 2017-1 EETC Class B
Debt Instrument [Line Items]
Estimated Fair Value	40.1	42.9
Estimated Fair Value \| Level 2 \| Convertible Notes \| 4.75% convertible notes due 2025
Debt Instrument [Line Items]
Estimated Fair Value	19.0	42.3
Estimated Fair Value \| Level 2 \| Convertible Notes \| 1.00% convertible notes due 2026
Debt Instrument [Line Items]
Estimated Fair Value	$ 240.0	$ 349.9