Commitments and Contingencies - Schedule of Commitments to Purchase Aircrafts (Details)	Jun. 30, 2018 commitment
Airbus A350
Long-term Purchase Commitment [Line Items]
Number of Firm Commitments	45
Boeing 737 MAX
Long-term Purchase Commitment [Line Items]
Number of Firm Commitments	155
Boeing 777-300ER
Long-term Purchase Commitment [Line Items]
Number of Firm Commitments	1
Boeing 787
Long-term Purchase Commitment [Line Items]
Number of Firm Commitments	18