Fair Value Measurements and Derivative Instruments - Balance Sheet (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Asset Derivatives
Asset Derivatives	$ 119,704		$ 188,576
Liability Derivatives
Liability Derivatives	107,340		100,260
Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives	104,120	[1]	173,229	[1]
Liability Derivatives
Liability Derivatives	84,685	[1]	77,629	[1]
Designated as Hedging Instrument | Collars | Other assets
Asset Derivatives
Asset Derivatives	19,565	[1]	22,172	[1]
Designated as Hedging Instrument | Collars | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	0	[1]	0	[1]
Not Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives	15,584		15,347
Liability Derivatives
Liability Derivatives	22,655		22,631
Interest rate swaps | Designated as Hedging Instrument | Other assets
Asset Derivatives
Asset Derivatives	26,971	[1]	56,571	[1]
Interest rate swaps | Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	59,353	[1]	66,920	[1]
Foreign currency forward contracts | Designated as Hedging Instrument | Other assets
Asset Derivatives
Asset Derivatives	14,036	[1]	13,783	[1]
Foreign currency forward contracts | Designated as Hedging Instrument | Derivative financial instruments
Asset Derivatives
Asset Derivatives	36,758	[1]	61,596	[1]
Foreign currency forward contracts | Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	4,086	[1]	0	[1]
Foreign currency forward contracts | Designated as Hedging Instrument | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	0	[1]	0	[1]
Foreign currency forward contracts | Not Designated as Hedging Instrument | Derivative financial instruments
Asset Derivatives
Asset Derivatives	15,345		15,347
Foreign currency forward contracts | Not Designated as Hedging Instrument | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	22,647		22,631
Fuel contracts | Designated as Hedging Instrument | Swaps | Other assets
Asset Derivatives
Asset Derivatives	2,808	[1]	8,205	[1]
Fuel contracts | Designated as Hedging Instrument | Swaps | Derivative financial instruments
Asset Derivatives
Asset Derivatives	3,982	[1]	10,902	[1]
Fuel contracts | Designated as Hedging Instrument | Swaps | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	13,897	[1]	9,052	[1]
Fuel contracts | Designated as Hedging Instrument | Swaps | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	7,349	[1]	1,657	[1]
Fuel contracts | Not Designated as Hedging Instrument | Swaps | Derivative financial instruments
Asset Derivatives
Asset Derivatives	239		0
Fuel contracts | Not Designated as Hedging Instrument | Swaps | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	0		0
Fuel contracts | Not Designated as Hedging Instrument | Options | Derivative financial instruments
Asset Derivatives
Asset Derivatives	0		0
Fuel contracts | Not Designated as Hedging Instrument | Options | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	$ 8		$ 0

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