Fair Value Measurements and Derivative Instruments - Derivatives Not Designated as Hedging Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives			$ (3,979)	$ (16,902)
Other income (expense)
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives	$ (23,776)	$ 11,197	(9,299)	(17,015)
Foreign currency forward contracts | Other income (expense)
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives	(23,703)	11,181	(9,248)	(16,902)
Fuel swaps | Fuel swaps | Other income (expense)
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives	$ (73)	$ 16	$ (51)	$ (113)