Fair Value Measurements and Derivative Instruments - Derivatives Not Designated as Hedging Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives			$ 56,836	$ (6,353)
Other expense
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives	$ 21,776	$ (3,636)	56,764	(12,936)
Foreign currency forward contracts | Other expense
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives	21,951	(2,464)	57,019	(11,712)
Fuel swaps | Other expense
Derivative Instruments
Amount of Gain (Loss) Recognized in Income on Derivatives	$ (175)	$ (1,172)	$ (255)	$ (1,224)