Fair Value Measurements and Derivative Instruments - Balance Sheet (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Asset Derivatives
Asset Derivatives		$ 391,116	$ 320,385
Liability Derivatives
Liability Derivatives		118,117	115,961
Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives	[1]	377,209	298,963
Liability Derivatives
Liability Derivatives	[1]	107,482	105,033
Notional Disclosures
Carrying Amount of the Hedged Assets/(Liabilities)		751,014	749,155
Cumulative amount of Fair Value Hedging Adjustment Included in the Carrying Amount of the Hedged Assets/(Liabilities)		(33,274)	(34,813)
Not Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives		13,907	21,422
Liability Derivatives
Liability Derivatives		10,635	10,928
Interest rate swaps | Designated as Hedging Instrument | Other assets
Asset Derivatives
Asset Derivatives	[1]	38,096	7,330
Interest rate swaps | Designated as Hedging Instrument | Other long-term liabilities
Liability Derivatives
Liability Derivatives	[1]	47,251	46,509
Foreign currency forward contracts | Designated as Hedging Instrument | Other assets
Asset Derivatives
Asset Derivatives	[1]	235,802	158,879
Foreign currency forward contracts | Designated as Hedging Instrument | Derivative financial instruments
Asset Derivatives
Asset Derivatives	[1]	42,688	68,352
Liability Derivatives
Liability Derivatives	[1]	1,390	0
Foreign currency forward contracts | Designated as Hedging Instrument | Other long-term liabilities
Liability Derivatives
Liability Derivatives	[1]	12,426	6,625
Foreign currency forward contracts | Not Designated as Hedging Instrument | Other assets
Asset Derivatives
Asset Derivatives		4,413	2,793
Foreign currency forward contracts | Not Designated as Hedging Instrument | Derivative financial instruments
Asset Derivatives
Asset Derivatives		4,361	9,945
Liability Derivatives
Liability Derivatives		2,369	2,933
Foreign currency forward contracts | Not Designated as Hedging Instrument | Other long-term liabilities
Liability Derivatives
Liability Derivatives		2,762	1,139
Fuel swaps | Designated as Hedging Instrument | Other assets
Asset Derivatives
Asset Derivatives	[1]	38,562	51,265
Fuel swaps | Designated as Hedging Instrument | Derivative financial instruments
Asset Derivatives
Asset Derivatives	[1]	22,061	13,137
Liability Derivatives
Liability Derivatives	[1]	31,235	38,488
Fuel swaps | Designated as Hedging Instrument | Other long-term liabilities
Liability Derivatives
Liability Derivatives	[1]	15,180	13,411
Fuel swaps | Not Designated as Hedging Instrument | Other assets
Asset Derivatives
Asset Derivatives		303	798
Fuel swaps | Not Designated as Hedging Instrument | Derivative financial instruments
Asset Derivatives
Asset Derivatives		4,830	7,886
Liability Derivatives
Liability Derivatives		5,320	6,043
Fuel swaps | Not Designated as Hedging Instrument | Other long-term liabilities
Liability Derivatives
Liability Derivatives		$ 184	$ 813

[1] Accounting Standard Codification 815-20 “Derivatives and Hedging.”