Summary of Significant Accounting Policies - Property and Equipment (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) aircraft	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Property, Plant and Equipment [Line Items]
Number of spare engines capitalized | aircraft	14
Number of flight simulators capitalized | aircraft	1
Depreciation, Depletion and Amortization, Nonproduction [Abstract]
Depreciation	$ 155,326	$ 129,412	$ 83,154
Amortization of capitalized software	6,574	6,029	3,143
Total depreciation and amortization	$ 225,264	176,727	140,152
Aircrafts, Major Spare Rotable Parts, Avionics, and Assemblies
Property, Plant and Equipment [Line Items]
Residual value, percentage	10.00%
Aircraft
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	15 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	$ 13,000	13,700
Capitalized software costs during the year	$ 5,900	12,000	1,400
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
Heavy maintenance and major overhaul
Depreciation, Depletion and Amortization, Nonproduction [Abstract]
Amortization of heavy maintenance	$ 63,364	$ 41,286	$ 53,855
Spare engines | Minimum
Property, Plant and Equipment [Line Items]
Operating leases, term	2 years
Spare engines | Maximum
Property, Plant and Equipment [Line Items]
Operating leases, term	14 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]
Operating leases, term	8 years
Aircraft | Maximum
Property, Plant and Equipment [Line Items]
Operating leases, term	18 years
A320 Family | Aircraft
Property, Plant and Equipment [Line Items]
Number of aircraft under finance lease | aircraft	2
A320 Family | Aircraft
Property, Plant and Equipment [Line Items]
Number of aircraft capitalized | aircraft	91