Commitments and Contingencies - Firm Commitments and Options to Purchase Aircraft (Details)	Mar. 31, 2020 commitment
Airbus A321XLR
Long-term Purchase Commitment [Line Items]
Number of firm commitments	50
Scheduled Aircraft Deliveries
Last Nine Months of 2020	0
2021	0
After 2021	50
Airbus A350
Long-term Purchase Commitment [Line Items]
Number of firm commitments	45
Scheduled Aircraft Deliveries
Last Nine Months of 2020	0
2021	0
After 2021	45
Boeing 737 MAX
Long-term Purchase Commitment [Line Items]
Number of firm commitments	171
Scheduled Aircraft Deliveries
Last Nine Months of 2020 (if order is lifted)	16
2021 (if order is lifted)	24
Boeing 787
Long-term Purchase Commitment [Line Items]
Number of firm commitments	19
Scheduled Aircraft Deliveries
Last Nine Months of 2020	11
2021	8
After 2021	0
Embraer E175
Long-term Purchase Commitment [Line Items]
Number of firm commitments	20
Scheduled Aircraft Deliveries
Last Nine Months of 2020	16
2021	4
After 2021	0