Financial Instruments and Risk Management - Narrative (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2015 aircraft derivative_instrument	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) derivative_instrument	Dec. 31, 2014 USD ($)
Derivative [Line Items]
Fuel federal excise tax				$ 9,300
Unrealized loss on interest rate derivative instruments		$ 0	$ 910	718
Unrealized gain (loss) on interest rate derivative instrument, tax		0	(550)	(423)
Loss reclassified from AOCI into income, tax		130	50	0
Accumulated other comprehensive loss		1,345	1,546
Airbus A321
Derivative [Line Items]
Number of aircraft protected by interest rate derivatives delivered | aircraft	3
Jet fuel options
Derivative [Line Items]
Payments for premiums on fuel option derivatives			$ 2,500	$ 9,700
Interest rate swap
Derivative [Line Items]
Number of interest rate derivatives settled | derivative_instrument	6		6
Accumulated other comprehensive loss		1,322	$ (1,500)
Interest rate swap | Cash flow hedge
Derivative [Line Items]
Unrealized loss on interest rate derivative instruments		0	900
Unrealized gain (loss) on interest rate derivative instrument, tax		0	600
Loss reclassified from AOCI into earnings		224	82
Loss reclassified from AOCI into income, tax		$ 130	$ 50