Fair Value Measurements and Derivative Instruments - Derivatives Not Designated as Hedging Instruments (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments
Amount of gain (loss) recognized in income on derivatives	$ (24,940)	$ (11,647)	$ (24,229)	$ (41,397)
Foreign currency forward contracts | Other income (expense)
Derivative Instruments
Amount of gain (loss) recognized in income on derivatives	(26,035)	(12,097)	(25,189)	(43,356)
Fuel swaps | Other income (expense)
Derivative Instruments
Amount of gain (loss) recognized in income on derivatives	1,095	(28)	974	155
Fuel swaps | Fuel cost
Derivative Instruments
Amount of gain (loss) recognized in income on derivatives	$ 0	$ 478	$ (14)	$ 1,804