Commitments and Contingencies - Aircraft Purchase Commitments By Aircraft (Details) - Future aircraft purchase commitments	Jun. 30, 2019 aircraft
Unrecorded Unconditional Purchase Obligation
Aircraft purchase commitments, minimum quantity required	275
A220-100
Unrecorded Unconditional Purchase Obligation
Aircraft purchase commitments, minimum quantity required	27
A220-300
Unrecorded Unconditional Purchase Obligation
Aircraft purchase commitments, minimum quantity required	50
A321-200
Unrecorded Unconditional Purchase Obligation
Aircraft purchase commitments, minimum quantity required	44
A321-200neo
Unrecorded Unconditional Purchase Obligation
Aircraft purchase commitments, minimum quantity required	100
A330-900neo
Unrecorded Unconditional Purchase Obligation
Aircraft purchase commitments, minimum quantity required	33
A350-900
Unrecorded Unconditional Purchase Obligation
Aircraft purchase commitments, minimum quantity required	12
CRJ-900
Unrecorded Unconditional Purchase Obligation
Aircraft purchase commitments, minimum quantity required	9