Debt and Other Obligations - Narrative (Details)					2 Months Ended	3 Months Ended		7 Months Ended	9 Months Ended
	Sep. 05, 2025	Aug. 21, 2025 USD ($)	Mar. 13, 2025 USD ($) aircraftEngine	Mar. 12, 2025 USD ($)	Mar. 12, 2025 USD ($)	Sep. 30, 2025 USD ($)	Jun. 30, 2025 USD ($)	Sep. 30, 2025 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2026 USD ($)	Mar. 31, 2025 USD ($)	Dec. 23, 2024 USD ($)
Debt Instrument [Line Items]
Repayments of debt					$ 634,506,000			$ 63,525,000	$ 151,517,000
Repayments of long-term debt					25,500,000	$ 21,400,000		63,500,000
Airbus
Debt Instrument [Line Items]
Future aircraft to be received | aircraftEngine			27
Aircraft Counterparties
Debt Instrument [Line Items]
Bankruptcy proceedings, rental holiday period	60 days
Exit secured notes
Debt Instrument [Line Items]
Amount of interest expense to be incurred if no bankruptcy								56,900,000
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
Amount of interest expense to be incurred if no bankruptcy								1,900,000
2030 Senior Notes | Debt Instrument, Redemption, Period One
Debt Instrument [Line Items]
Debt instrument, redemption price (as a percent)			100.00%
Minimum number of days after effective date, option to redeem			90 days
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%
2030 Senior Notes | Exit secured notes
Debt Instrument [Line Items]
Amount of interest expense to be incurred if no bankruptcy						26,100,000
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
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 | 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, maximum borrowing capacity						275,000,000		$ 275,000,000
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
Amount of interest expense to be incurred if no bankruptcy						1,900,000
Revolving credit facility | Exit Revolving Credit Facility | Line of Credit | Forecast
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity										$ 250,000,000
Revolving credit facility | Exit 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 | Exit 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 RCF Commitments | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity						275,000,000		$ 275,000,000
Proceeds from lines of credit		$ 275,000,000
Revolving credit facility | Uncommitted Incremental Revolving Credit Facility | Line of Credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity						$ 25,000,000		$ 25,000,000
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
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