Commitments and Contingencies - Schedule of Future Aircraft Operating Leases (Details)	Dec. 31, 2017 aircraft
Long-term Purchase Commitment [Line Items]
2018	10
2019	15
2020	16
2021	18
Total future aircraft to be received	59
Airbus | A320
Long-term Purchase Commitment [Line Items]
2018	5
2019	1
2020
Total future aircraft to be received	6
Airbus | A320NEO
Long-term Purchase Commitment [Line Items]
2019	14
2020	16
2021	18
Total future aircraft to be received	48
Airbus | A321
Long-term Purchase Commitment [Line Items]
2018	5
2019
Total future aircraft to be received	5