Summary of Significant Accounting Policies - Property and Equipment (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) aircraft_Engine flightSimulator aircraft	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Property, Plant and Equipment [Line Items]
Number of spare engines capitalized | aircraft_Engine	16
Number of flight simulators capitalized | flightSimulator	1
Depreciation, Depletion and Amortization, Nonproduction [Abstract]
Depreciation	$ 179,470	$ 155,326	$ 129,412
Amortization of capitalized software	10,191	6,574	6,029
Total depreciation and amortization	$ 278,588	225,264	176,727
Spare engines
Property, Plant and Equipment [Line Items]
Number of aircraft under operating lease | aircraft_Engine	8
Minimum | Aircraft
Property, Plant and Equipment [Line Items]
Operating leases, term	8 years
Maximum | Aircraft
Property, Plant and Equipment [Line Items]
Operating leases, term	18 years
Aircrafts, Major Spare Rotable Parts, Avionics, and Assemblies
Property, Plant and Equipment [Line Items]
Residual value, percentage	10.00%
Aircraft, engines and flight simulators
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	25 years
Spare rotables and flight assemblies | Minimum
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	7 years
Spare rotables and flight assemblies | Maximum
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	25 years
Other equipment and vehicles | Minimum
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	5 years
Other equipment and vehicles | Maximum
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	7 years
Internal use software
Depreciation, Depletion and Amortization, Nonproduction [Abstract]
Capitalized computer software, net	$ 24,300	13,000
Capitalized software costs during the year	$ 21,500	$ 5,900	$ 12,000
Internal use software | Minimum
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	3 years
Internal use software | Maximum
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	10 years
Spare engines | Minimum
Property, Plant and Equipment [Line Items]
Operating leases, term	12 years
Spare engines | Maximum
Property, Plant and Equipment [Line Items]
Operating leases, term	16 years
Buildings
Property, Plant and Equipment [Line Items]
Depreciable lives used for the principal depreciable asset classifications	30 years
Aircraft | Minimum
Property, Plant and Equipment [Line Items]
Finance lease contract term	8 years
Aircraft | Maximum
Property, Plant and Equipment [Line Items]
Finance lease contract term	18 years
A320 Family | Aircraft
Property, Plant and Equipment [Line Items]
Number of aircraft under operating lease | aircraft	56
A320 Family | Aircraft
Property, Plant and Equipment [Line Items]
Number of aircraft capitalized | aircraft	101