Fair Value Measurements and Derivative Instruments (Balance Sheet) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Asset Derivatives
Asset Derivatives	$ 63,981	$ 188,576
Liability Derivatives
Liability Derivatives	767,635	100,260
Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives	63,981	173,229
Liability Derivatives
Liability Derivatives	767,635	77,629
Designated as Hedging Instrument | Collars | Other Assets
Asset Derivatives
Asset Derivatives	0	22,172
Designated as Hedging Instrument | Collars | Derivative Financial Instruments
Liability Derivatives
Liability Derivatives	21,855	0
Designated as Hedging Instrument | Collars | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	0	0
Not Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives	0	15,347
Liability Derivatives
Liability Derivatives	0	22,631
Interest rate swaps | Designated as Hedging Instrument | Other Assets
Asset Derivatives
Asset Derivatives	0	56,571
Interest rate swaps | Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	65,768	66,920
Foreign currency forward contracts | Designated as Hedging Instrument | Other Assets
Asset Derivatives
Asset Derivatives	63,981	13,783
Foreign currency forward contracts | Designated as Hedging Instrument | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	0	61,596
Liability Derivatives
Liability Derivatives	17,619	0
Foreign currency forward contracts | Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	164,627	0
Foreign currency forward contracts | Not Designated as Hedging Instrument
Liability Derivatives
Liability Derivatives	0	22,631
Foreign currency forward contracts | Not Designated as Hedging Instrument | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	0	15,347
Fuel contracts | Designated as Hedging Instrument | Fuel Swaps | Other Assets
Asset Derivatives
Asset Derivatives	0	8,205
Fuel contracts | Designated as Hedging Instrument | Fuel Swaps | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	0	10,902
Liability Derivatives
Liability Derivatives	227,512	1,657
Fuel contracts | Designated as Hedging Instrument | Fuel Swaps | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	$ 270,254	$ 9,052