Commitments and Contingencies - Aircraft Commitments by Fleet Type (Details) (Details) - Future aircraft purchase commitments	Jun. 30, 2021 aircraft
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	259
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	7
A321-200neo
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	125
A330-900neo
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	26
A350-900
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	27
Number of lease commitments included in purchase commitment	7
B737-900ER
Future Purchase Commitments
Aircraft purchase commitments, minimum quantity required	29