Fair Value Measurements and Derivative Instruments (Details 6) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Asset Derivatives
Asset Derivatives	$ 128,484	$ 96,489
Liability Derivatives
Liability Derivatives	106,262	85,119
Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives	117,420	83,797
Liability Derivatives
Liability Derivatives	88,169	64,939
Designated as Hedging Instrument | Collars | Other assets
Asset Derivatives
Asset Derivatives	14,529	8,974
Not Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives	11,064	12,692
Liability Derivatives
Liability Derivatives	18,093	20,180
Interest rate swaps | Designated as Hedging Instrument | Other assets
Asset Derivatives
Asset Derivatives	39,974	5,099
Interest rate swaps | Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	60,541	55,471
Foreign currency forward contracts | Designated as Hedging Instrument | Other assets
Asset Derivatives
Asset Derivatives	24,494	11,564
Foreign currency forward contracts | Designated as Hedging Instrument | Derivative financial instruments
Asset Derivatives
Asset Derivatives	23,474	951
Foreign currency forward contracts | Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives		1,000
Foreign currency forward contracts | Designated as Hedging Instrument | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives		338
Foreign currency forward contracts | Not Designated as Hedging Instrument | Other assets
Asset Derivatives
Asset Derivatives	98	4,440
Foreign currency forward contracts | Not Designated as Hedging Instrument | Derivative financial instruments
Asset Derivatives
Asset Derivatives	8,162
Foreign currency forward contracts | Not Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	10,242	11,475
Foreign currency forward contracts | Not Designated as Hedging Instrument | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	5,208
Fuel contracts | Designated as Hedging Instrument | Swaps | Other assets
Asset Derivatives
Asset Derivatives	1,094	8,585
Fuel contracts | Designated as Hedging Instrument | Swaps | Derivative financial instruments
Asset Derivatives
Asset Derivatives	13,855	48,624
Fuel contracts | Designated as Hedging Instrument | Swaps | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	23,367	6,369
Fuel contracts | Designated as Hedging Instrument | Swaps | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	4,261	1,761
Fuel contracts | Not Designated as Hedging Instrument | Swaps | Derivative financial instruments
Asset Derivatives
Asset Derivatives	138
Fuel contracts | Not Designated as Hedging Instrument | Swaps | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives		475
Fuel contracts | Not Designated as Hedging Instrument | Options | Derivative financial instruments
Asset Derivatives
Asset Derivatives	2,666	8,252
Fuel contracts | Not Designated as Hedging Instrument | Options | Accrued expenses and other liabilities
Liability Derivatives
Liability Derivatives	$ 2,643	$ 8,230