Commitments and Contingencies - Aircraft Commitments by Fleet Type (Details) (Details) - Future aircraft purchase commitments	Sep. 30, 2021 aircraft
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	283
A220-100
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	4
A220-300
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	41
A321-200
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	4
A321-200neo
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	155
A330-900neo
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	26
A350-900
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	26
Number of lease commitments included in purchase commitment	6
B-737-900ER
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	27