Fair Value Measurements and Derivative Instruments (Balance Sheet) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Asset Derivatives
Asset Derivatives	$ 188,576	$ 96,489
Liability Derivatives
Liability Derivatives	100,260	85,119
Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives	173,229	83,797
Liability Derivatives
Liability Derivatives	77,629	64,939
Designated as Hedging Instrument | Collars | Other Assets
Asset Derivatives
Asset Derivatives	22,172	8,974
Designated as Hedging Instrument | Collars | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	0	0
Not Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives	15,347	12,692
Liability Derivatives
Liability Derivatives	22,631	20,180
Not Designated as Hedging Instrument | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	15,347	0
Interest rate swaps | Designated as Hedging Instrument | Other Assets
Asset Derivatives
Asset Derivatives	56,571	5,099
Interest rate swaps | Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	66,920	55,471
Foreign currency forward contracts | Designated as Hedging Instrument | Other Assets
Asset Derivatives
Asset Derivatives	13,783	11,564
Foreign currency forward contracts | Designated as Hedging Instrument | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	61,596	951
Foreign currency forward contracts | Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	0	1,000
Foreign currency forward contracts | Designated as Hedging Instrument | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	0	338
Foreign currency forward contracts | Not Designated as Hedging Instrument
Liability Derivatives
Liability Derivatives	22,631	0
Foreign currency forward contracts | Not Designated as Hedging Instrument | Other Assets
Asset Derivatives
Asset Derivatives	0	4,440
Foreign currency forward contracts | Not Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	0	11,475
Fuel contracts | Designated as Hedging Instrument | Swaps | Other Assets
Asset Derivatives
Asset Derivatives	8,205	8,585
Fuel contracts | Designated as Hedging Instrument | Swaps | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	10,902	48,624
Fuel contracts | Designated as Hedging Instrument | Swaps | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	9,052	6,369
Fuel contracts | Designated as Hedging Instrument | Swaps | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	1,657	1,761
Fuel contracts | Not Designated as Hedging Instrument | Swaps | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	0	0
Fuel contracts | Not Designated as Hedging Instrument | Swaps | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	0	475
Fuel contracts | Not Designated as Hedging Instrument | Options | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	0	8,252
Fuel contracts | Not Designated as Hedging Instrument | Options | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	$ 0	$ 8,230