Financial Instruments and Risk Management (Details) $ in Thousands, gal in Millions	12 Months Ended			54 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($) $ / gal gal	Dec. 31, 2013 USD ($)	Dec. 31, 2013 USD ($)	Sep. 30, 2015 USD ($) derivative_instrument aircraft
Components Of Aircraft Fuel Expense [Abstract]
Into-plane fuel cost	$ 454,747	$ 608,033	$ 542,523
Gain (Loss) on Hedging Activity	(10,580)	(995)	(8,958)
Unrealized losses (gains) related to fuel derivative contracts, net	(3,880)	3,881	265
Aircraft fuel	461,447	$ 612,909	551,746
Fuel Federal Excise Tax				$ 9,300
Jet fuel consumption protected, fuel derivative (gallons) | gal		88.7
Anticipated jet fuel consumption protected by hedges (percent)		35.00%
Unrealized gain (loss) on interest rate derivative instruments, net of deferred tax expense (benefit) of ($500), ($423) and $0	(828)	$ (718)	0
Derivative instrument, change in fair value recorded within accumulated other comprehensive income, deferred tax	(500)	$ (423)	$ 0
Airbus A321
Components Of Aircraft Fuel Expense [Abstract]
Number of aircraft protected by interest rate derivatives scheduled for delivery | aircraft					3
Options held | Fuel
Components Of Aircraft Fuel Expense [Abstract]
Derivative, weighted-average ceiling price | $ / gal		2.07
Jet fuel options
Derivative [Line Items]
Payments of derivative issuance costs	2,500	$ 9,700
Interest rate swap
Components Of Aircraft Fuel Expense [Abstract]
Number of interest rate derivatives settled | derivative_instrument					6
Notional amount					$ 120,000
Interest rate swap | Cash flow hedge
Components Of Aircraft Fuel Expense [Abstract]
Unrealized gain (loss) on interest rate derivative instruments, net of deferred tax expense (benefit) of ($500), ($423) and $0	828	718
Derivative instrument, change in fair value recorded within accumulated other comprehensive income, deferred tax	$ 500	$ 423