Fair Value Measurements and Derivative Instruments (Derivatives Not Designated as Hedging Instruments) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative instruments disclosure
Amount of Gain (Loss) Recognized in Income on Derivatives	$ 60,819	$ (52,029)
Foreign exchange contracts | Other income (expense)
Derivative instruments disclosure
Amount of Gain (Loss) Recognized in Income on Derivatives	61,952	(51,029)
Fuel contracts | Other income (expense)
Derivative instruments disclosure
Amount of Gain (Loss) Recognized in Income on Derivatives	$ (1,133)	$ (1,000)