Fair Value Measurements and Derivative Instruments - Derivatives Not Designated as Hedging Instruments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives	$ 1,890	$ (8,523)
Other income (expense)
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives	659	(8,344)
Foreign exchange contracts | Other income (expense)
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives	1,881	(8,611)
Fuel contracts | Fuel swaps | Other income (expense)
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives	(1,222)	109
Fuel contracts | Options | Other income (expense)
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives	$ 0	$ 158