Commitments and Contingencies - Narrative (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021 USD ($)	Nov. 04, 2021 aircraft	Dec. 31, 2020 USD ($)
Long-term Purchase Commitment [Line Items]
Minimum aircraft delivery delays that could trigger lessee cancellation clauses	1 year
Purchase agreements, termination commencement period	1 year
Deposits on flight equipment purchases | $	$ 1,597,597		$ 1,800,119
Boeing 737-7/8/9 MAX | Subsequent Event
Long-term Purchase Commitment [Line Items]
Purchase commitment, number of aircraft cancelled | aircraft		23
Boeing 787-9/10 | Subsequent Event
Long-term Purchase Commitment [Line Items]
Purchase commitment, number of aircraft cancelled | aircraft		3
Aircrafts
Long-term Purchase Commitment [Line Items]
Deposits on flight equipment purchases | $	$ 1,600,000		$ 1,800,000