Commitments and Contingencies - Schedule of Future Aircraft Operating Leases (Details) $ in Millions	Sep. 30, 2019 USD ($) aircraft
Long-term Purchase Commitment [Line Items]
Remainder of 2019	9
2020	20
2021	27
Future aircraft to be received	56
Airbus [Member] | A-320-Neo [Member]
Long-term Purchase Commitment [Line Items]
Remainder of 2019	7
2020	15
2021	20
Future aircraft to be received	42
Third Party Lessor [Member] | A320 Family [Member]
Long-term Purchase Commitment [Line Items]
Operating Leases Future Minimum Payments for Aircraft Scheduled for Delivery, Remainder of Fiscal Year | $	$ 0.8
Operating leases Future Minimum Payments for Aircraft, Due in Two Years | $	15.0
Operating leases Future Minimum Payments for Aircraft, Due in Three Years | $	42.0
Operating leases Future Minimum Payments for Aircraft, Due in Four Years | $	47.8
Operating leases Future Minimum Payments for Aircraft, Due in Five Years | $	47.8
Operating leases Future Minimum Payments for Aircraft, Due Thereafter | $	$ 420.4
Third Party Lessor [Member] | A-320 [Member]
Long-term Purchase Commitment [Line Items]
Remainder of 2019	2
2020	0
2021	0
Future aircraft to be received	2
Third Party Lessor [Member] | A-320-Neo [Member]
Long-term Purchase Commitment [Line Items]
Remainder of 2019	0
2020	5
2021	7
Future aircraft to be received	12