Commitments and Contingencies - Firm Commitments and Options to Purchase Aircraft (Details)	Mar. 31, 2021 commitment
Airbus A321XLR
Long-term Purchase Commitment [Line Items]
Number of firm commitments	50
Scheduled Aircraft Deliveries
Last Nine Months of 2021	0
2022	0
After 2022	50
Airbus A350
Long-term Purchase Commitment [Line Items]
Number of firm commitments	45
Scheduled Aircraft Deliveries
Last Nine Months of 2021	0
2022	0
After 2022	45
Boeing 737 MAX
Long-term Purchase Commitment [Line Items]
Number of firm commitments	180
Scheduled Aircraft Deliveries
Last Nine Months of 2021	13
2022	40
After 2022	127
Boeing 787
Long-term Purchase Commitment [Line Items]
Number of firm commitments	9
Scheduled Aircraft Deliveries
Last Nine Months of 2021	9
2022	0
After 2022	0
Embraer E175
Long-term Purchase Commitment [Line Items]
Number of firm commitments	4
Scheduled Aircraft Deliveries
Last Nine Months of 2021	4
2022	0
After 2022	0