Fair Value Measurements and Derivative Instruments - Derivatives Not Designated as Hedging Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives			$ 34,988	$ (3,979)
Other expense
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives	$ 21,236	$ (23,776)	34,988	(9,299)
Foreign currency forward contracts | Other expense
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives	21,256	(23,703)	35,068	(9,248)
Fuel swaps | Other expense
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives	$ (20)	$ (73)	$ (80)	$ (51)