Financial Instruments and Risk Management - Narrative (Details) $ in Thousands, gal in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($) derivative_instrument aircraft $ / gal gal	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) derivative_instrument aircraft $ / gal gal	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) $ / gal gal
Derivative [Line Items]
Anticipated jet fuel consumption protected by hedges (in gallons) | gal	25.5		25.5		88.7
Anticipated jet fuel consumption protected by hedges (as a percent)	19.00%		19.00%		35.00%
Unrealized gain (loss) on interest rate derivative instruments, net of deferred taxes of $749, $0, ($191) and $0	$ 1,238	$ 0	$ (356)	$ 0
Unrealized gain (loss) on interest rate derivative instruments, tax	$ 749	$ 0	$ (191)	$ 0
Airbus A321 [Member] | 2015 [Member]
Derivative [Line Items]
Number of Aircraft protected by Interest Rate Derivatives Schedule for Delivery | aircraft	3		3
Interest Rate Swap [Member]
Derivative [Line Items]
Number of Interest Rate Derivatives Held | derivative_instrument	6		6
Derivative, Notional Amount	$ 120,000		$ 120,000
Interest Rate Derivative Liabilities, at Fair Value					$ 1,100
Interest Rate Swap [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Unrealized gain (loss) on interest rate derivative instruments, tax	$ (700)		$ 200
Options Held [Member] | Fuel [Member]
Derivative [Line Items]
Derivative contract, weighted average ceiling price (in USD per gallon) | $ / gal	1.93		1.93		2.07
Fair Value, Measurements, Recurring [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Interest rate swaps	$ 1,700		$ 1,700		$ 1,100
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Interest rate swaps	1,700		1,700		$ 1,100
Interest Rate Derivative Liabilities, at Fair Value	$ 1,700		$ 1,700