Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2015

Depreciable lives used for the principal depreciable asset classifications

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



	Year Ended December 31,
	2015		2014		2013
	(in thousands)
Depreciation	$	30,797	$	11,169	$	8,340
Amortization of heavy maintenance	43,111		35,802		23,607
Total depreciation and amortization	$	73,908	$	46,971	$	31,947

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



	Estimated Useful Life
Aircraft	25 years
Spare rotables and flight assemblies	7 to 15 years
Other equipment and vehicles	5 to 7 years
Internal use software	3 to 10 years
Capital lease	Lease term
Leasehold improvements	Lesser of lease term or estimated useful life of the improvement

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 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, 2015	$	58,005	$	35,938
December 31, 2014	33,819		28,140
December 31, 2013	28,496		23,124

Primary components of non-ticket revenue and the revenue recognition method utilized for each service or product

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



		Year Ended December 31,
Non-ticket revenue	Recognition method	2015		2014		2013
		(in thousands)
Baggage	Time of departure	$	381,386	$	318,103	$	275,958
Passenger usage fee	Time of departure	298,092		221,992		188,911
Advance seat selection	Time of departure	97,786		76,270		59,241
Service charges for changes and cancellations	When itinerary is changed	43,756		38,388		32,546
Other		151,105		131,855		111,711
Non-ticket revenue		$	972,125	$	786,608	$	668,367

Aircraft maintenance expense

The table below summarizes the extent to which the Company’s maintenance costs are rate capped due to flight hour maintenance contracts:



	Year Ended December 31,
	2015		2014		2013
	(in thousands)
Flight hour-based maintenance expense	$	41,818	$	35,675	$	30,322
Non-flight hour-based maintenance expense	38,630		38,281		29,821
Total maintenance, materials and repairs	$	80,448	$	73,956	$	60,143