Commitments and Contingencies - Aircraft-Related Commitments and Financing Arrangements and Other Commitments (Details)	Mar. 31, 2025 USD ($) aircraft aircraft_engine aircraftEngine
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of delivered aircraft with secured debt financing commitments | aircraft	67
Aircraft-Related Secured Debt
Unrecorded Unconditional Purchase Obligation [Line Items]
Interest commitments, remainder of fiscal year	$ 61,600,000
Interest commitments, 2026	81,100,000
Interest commitments, 2027	69,000,000.0
Interest commitments, 2028	50,100,000
Interest commitments, 2029	35,300,000
Interest commitments, 2030 and thereafter	105,400,000
Unsecured term loans
Unrecorded Unconditional Purchase Obligation [Line Items]
Interest commitments, remainder of fiscal year	1,700,000
Interest commitments, 2026	3,400,000
Interest commitments, 2027	3,400,000
Interest commitments, 2028	3,400,000
Interest commitments, 2029	3,400,000
Interest commitments, 2030 and thereafter	3,700,000
Exit Secured Notes
Unrecorded Unconditional Purchase Obligation [Line Items]
Interest commitments, remainder of fiscal year	55,100,000
Interest commitments, 2026	70,500,000
Interest commitments, 2027	73,300,000
Interest commitments, 2028	76,300,000
Interest commitments, 2029	79,400,000
Interest commitments, 2030 and thereafter	24,200,000
Aircraft and Related Flight Equipment
Unrecorded Unconditional Purchase Obligation [Line Items]
Committed expenditures, remainder of fiscal year	63,200,000
Committed expenditures, 2026	12,300,000
Committed expenditures, 2027	183,000,000.0
Committed expenditures, 2028	297,800,000
Committed expenditures, 2029	1,124,300,000
Committed expenditures, 2030 and thereafter	1,857,800,000
Non-aircraft Related Commitments
Unrecorded Unconditional Purchase Obligation [Line Items]
Committed expenditures, remainder of fiscal year	36,400,000
Committed expenditures, 2026	26,900,000
Committed expenditures, 2027	20,500,000
Committed expenditures, 2028	2,900,000
Committed expenditures, 2029	100,000
Committed expenditures, 2030 and thereafter	$ 0
Airbus
Unrecorded Unconditional Purchase Obligation [Line Items]
Future aircraft to be received | aircraftEngine	27
Third Party Lessor | A320 and A321
Unrecorded Unconditional Purchase Obligation [Line Items]
Aircraft rent commitments, remainder of fiscal year	$ 11,100,000
Aircraft rent commitments, 2026	18,300,000
Aircraft rent commitments, 2027	80,900,000
Aircraft rent commitments, 2028	178,300,000
Aircraft rent commitments, 2029	225,500,000
Aircraft rent commitments, 2030 and beyond	$ 2,192,500,000
2024 Through 2031 | PurePower PW1100G-JM Engine
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of spare aircraft engines ordered | aircraft_engine	16
2024 Through 2031 | Airbus
Unrecorded Unconditional Purchase Obligation [Line Items]
Future aircraft to be received | aircraft	53
Number of aircraft without secured financing commitments scheduled for delivery | aircraft	52
Through 2025 | Airbus
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of aircraft with secured debt financing commitments scheduled for delivery | aircraft	1
2024 Through 2028 | Third Party Lessor | A320 and A321
Unrecorded Unconditional Purchase Obligation [Line Items]
Future aircraft to be received | aircraft	39