Commitments and Contingencies - Firm Commitments and Options to Purchase Aircraft (Details)	Sep. 30, 2020 commitment aircraft
Airbus A321XLR
Long-term Purchase Commitment [Line Items]
Number of firm commitments | commitment	50
Scheduled Aircraft Deliveries
Last Three Months of 2020	0
2021	0
2022	0
After 2022	50
Airbus A350
Long-term Purchase Commitment [Line Items]
Number of firm commitments | commitment	45
Scheduled Aircraft Deliveries
Last Three Months of 2020	0
2021	0
2022	0
After 2022	45
Boeing 737 MAX
Long-term Purchase Commitment [Line Items]
Number of firm commitments | commitment	171
Scheduled Aircraft Deliveries
Last Three Months of 2020	16
2021	24
2022	0
After 2022	131
Boeing 787
Long-term Purchase Commitment [Line Items]
Number of firm commitments | commitment	11
Scheduled Aircraft Deliveries
Last Three Months of 2020	3
2021	8
2022	0
After 2022	0
Embraer E175
Long-term Purchase Commitment [Line Items]
Number of firm commitments | commitment	15
Scheduled Aircraft Deliveries
Last Three Months of 2020	11
2021	4
2022	0
After 2022	0