Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Depreciable Lives Used for the Principal Depreciable Asset Classifications and Components of Depreciation and Amortization

The depreciable lives used for the principal depreciable asset classifications are:

	Estimated Useful Life
Aircraft, engines and flight simulators	25
Spare rotables and flight assemblies	7 to 25 years
Other equipment and vehicles	5 to 7 years
Internal use software	3 to 10 years
Finance leases	Lease term or estimated useful life of the asset
Leasehold improvements	Lesser of lease term or estimated useful life of the improvement
Buildings	Lesser of lease term or 30 years

The following table illustrates the components of depreciation and amortization expense:

	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Depreciation	$	179,470	$	155,326	$	129,412
Amortization of heavy maintenance	88,927		63,364		41,286
Amortization of capitalized software	10,191		6,574		6,029
Total depreciation and amortization	$	278,588	$	225,264	$	176,727

Primary Components of Non-fare Revenue and the Revenue Recognition Method Utilized for Each Service or Product

The following table summarizes the primary components of the Company's non-fare revenue and the revenue recognition method utilized for each service or product:

		Year Ended December 31,
Non-fare revenue	Recognition method	2020		2019		2018
		(in thousands)
Baggage	Time of departure	$	404,896	$	734,243	$	620,154
Passenger usage fee	Time of departure	358,561		669,177		531,459
Advance seat selection	Time of departure	125,213		228,876		180,012
Other		120,638		238,454		224,283
Non-fare revenue		$	1,009,308	$	1,870,750	$	1,555,908

Total Cash Proceeds Received from the Sale of Mileage Credit

The following table illustrates total cash proceeds received from the sale of mileage credits and the portion of such proceeds recognized in non-ticket revenue immediately as marketing component:

	Consideration received from credit card mile programs		Portion of proceeds recognized immediately as marketing component
Year Ended	(in thousands)
December 31, 2020	$	33,201	$	25,918
December 31, 2019	48,136		37,151
December 31, 2018	39,194		30,353

Aircraft Maintenance Expense

The table below summarizes the components of the Company’s maintenance cost:

	Year Ended December 31,
	2020		2019		2018
	(in thousands)
Flight hour-based maintenance expense	$	52,092	$	78,253	$	68,039
Non-flight hour-based maintenance expense	59,135		65,322		61,039
Total maintenance, materials and repairs	$	111,227	$	143,575	$	129,078