Financial Instruments and Risk Management - Narrative (Details) (USD $)	3 Months Ended
	Mar. 31, 2015 gal	Mar. 31, 2014	Dec. 31, 2014 gal
Derivative [Line Items]
Anticipated jet fuel consumption protected by hedges (in gallons)	70,300,000		88,700,000
Anticipated jet fuel consumption protected by hedges (as a percent)	34.70%		35.00%
Unrealized gain (loss) on interest rate derivative instruments, net of deferred taxes of $940 and $0	$ (1,594,000)	$ 0
Unrealized gain (loss) on interest rate derivative instruments, tax	940,000	0
Airbus A321 [Member] | 2015 [Member]
Derivative [Line Items]
Number of Aircraft protected by Interest Rate Derivatives Schedule for Delivery	3
Interest Rate Swap [Member]
Derivative [Line Items]
Number of Interest Rate Derivatives Held	6
Derivative, Notional Amount	120,000,000
Interest Rate Derivative Liabilities, at Fair Value	3,700,000
Interest Rate Swap [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Unrealized gain (loss) on interest rate derivative instruments, tax	$ 900,000
Options Held [Member] | Fuel [Member]
Derivative [Line Items]
Derivative contract, weighted average ceiling price (in USD per gallon)	1.91		2.07