Debt and Other Obligations - Narrative (Details)			1 Months Ended	2 Months Ended	3 Months Ended	4 Months Ended	6 Months Ended
	Mar. 13, 2025 USD ($) aircraftEngine	Mar. 12, 2025 USD ($)	Mar. 31, 2025 USD ($)	Mar. 12, 2025 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2024 USD ($)	Sep. 30, 2026 USD ($)	Dec. 31, 2024 USD ($)	Dec. 23, 2024 USD ($)	Mar. 30, 2020 USD ($)
Debt Instrument [Line Items]
Repayments of debt				$ 634,506,000		$ 42,129,000	$ 119,632,000
Liabilities subject to compromise		$ 1,600,000,000		1,600,000,000	$ 0	0			$ 1,635,104,000
Repayments of long-term debt				$ 25,500,000	35,900,000	$ 42,100,000
Airbus
Debt Instrument [Line Items]
Future aircraft to be received | aircraftEngine	27
Enhanced Equipment Trust Certificate
Debt Instrument [Line Items]
Debt instrument, interest rate (as a percent)	11.00%
Revolving credit facility due in 2026 | Revolving credit facility
Debt Instrument [Line Items]
Repayments of lines of credit		$ 300,000,000
2030 Senior Notes | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Minimum number of days after effective date, option to redeem	90 days
Debt instrument, redemption price (as a percent)	100.00%
2030 Senior Notes | Debt Instrument, Redemption, Period Two
Debt Instrument [Line Items]
Debt instrument, redemption price (as a percent)	6.00%
2030 Senior Notes | Debt Instrument, Redemption, Period Three
Debt Instrument [Line Items]
Debt instrument, redemption price (as a percent)	8.00%
2030 Senior Notes | Debt Instrument, Redemption, Period Four
Debt Instrument [Line Items]
Debt instrument, redemption price (as a percent)	4.00%
2030 Senior Notes | Secured Debt
Debt Instrument [Line Items]
Principal amount	$ 840,000,000.0
Stated interest rate percentage, cash	8.00%
Stated interest rate percentage, paid-in-kind	4.00%
Interest rate calculation basis, number of days in year	360 days
Interest rate calculation basis, number of days in each month	30 days
2030 Senior Notes | Secured Debt | Maximum
Debt Instrument [Line Items]
Stated interest rate percentage	12.00%
2030 Senior Notes | Secured Debt | Minimum
Debt Instrument [Line Items]
Stated interest rate percentage	11.00%
Class B(R) 2025-1 EETC | Enhanced Equipment Trust Certificate
Debt Instrument [Line Items]
Principal amount			$ 215,000,000
2017-1 EETC Class B | Enhanced Equipment Trust Certificate
Debt Instrument [Line Items]
Repayments of debt					$ 43,000,000
8.00% Senior Secured Notes | Secured Debt
Debt Instrument [Line Items]
Stated interest rate percentage		8.00%		8.00%	8.00%	8.00%	8.00%
Liabilities subject to compromise					$ 0	$ 0			$ 1,110,000,000
DIP Facility | Term Loan
Debt Instrument [Line Items]
Repayments of long-term debt						309,000,000
Revolving credit facility due in 2028 | Revolving credit facility
Debt Instrument [Line Items]
Repayments of long-term debt						300,000,000
Revolving credit facility | Line of Credit | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)			3.25%
Revolving credit facility | Line of Credit | Base Rate
Debt Instrument [Line Items]
Basis spread on variable rate (as a percent)			2.25%
Revolving credit facility | Exit Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity					300,000,000	300,000,000
Revolving credit facility | Exit Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, remaining borrowing capacity					275,000,000	275,000,000
Revolving credit facility | Revolving credit facility due in 2026 | Line of Credit
Debt Instrument [Line Items]
Debt instrument covenant, unrestricted cash and cash equivalents, short-term securities and unused commitments available on all revolving credit facilities											$ 500,000,000
Debt instrument covenant, maximum amount of unused commitments											$ 300,000,000
Debt covenant, collateral coverage ratio											1.0
Revolving credit facility | Exit RCF Commitments
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity					275,000,000	275,000,000
Revolving credit facility | Exit RCF Commitments | Forecast
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity								$ 250,000,000
Revolving credit facility | Uncommitted Incremental Revolving Credit Facility
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity					$ 25,000,000	$ 25,000,000
Revolving credit facility | DIP Credit Agreement and Facility | Line of Credit
Debt Instrument [Line Items]
Principal amount										$ 300,000,000
Debt issuance fee										$ 9,000,000
Revolving credit facility | Revolving credit facility due in 2030 | Line of Credit
Debt Instrument [Line Items]
Debt instrument covenant, unrestricted cash and cash equivalents, short-term securities and unused commitments available on all revolving credit facilities											$ 450,000,000
Debt instrument covenant, maximum amount of unused commitments											$ 300,000,000