Financial Derivative Instruments - Risk Management (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Derivative instrument
Gains (losses) on fuel derivatives recorded as Nonoperating income (expense)	$ 2,026	$ 6,285	$ (3,661)	$ (614)
Derivatives Not Designated as Hedging Instruments | Fuel derivative contracts
Derivative instrument
Losses realized at settlement	(16,553)	(2,009)	(31,144)	(1,899)
Reversal of prior period unrealized amounts	16,327	2,625	29,313	(1,613)
Unrealized gains (losses) that will settle in future periods	2,252	5,669	(1,830)	2,898
Gains (losses) on fuel derivatives recorded as Nonoperating income (expense)	$ 2,026	$ 6,285	(3,661)	$ (614)
Derivatives Designated as Hedging Instruments | Foreign Currency Derivatives
Derivative instrument
Accumulated other comprehensive income (loss) expected to be reclassified to earnings in the next 12 months			$ 13,600
Reclassification estimated time period			12 months