Commitments and Contingencies - Aircraft Purchase Commitments By Aircraft (Details) - Future aircraft purchase commitments	Sep. 30, 2019 aircraft
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	258
A220-100
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	20
A220-300
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	50
A321-200
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	33
A321-200neo
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	100
A330-900neo
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	31
A350-900
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	16
CRJ-900
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	8