Fair Value Measurements and Derivative Instruments (Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Asset Derivatives
Asset Derivatives	$ 19,397	$ 134,574
Liability Derivatives
Liability Derivatives	373,497	1,044,292
Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives	18,854	93,996
Liability Derivatives
Liability Derivatives	356,029	1,020,774
Not Designated as Hedging Instrument
Asset Derivatives
Asset Derivatives	543	40,578
Liability Derivatives
Liability Derivatives	17,468	23,518
Interest rate swaps | Designated as Hedging Instrument | Other Assets
Asset Derivatives
Asset Derivatives	5,246	0
Interest rate swaps | Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	57,679	67,371
Foreign currency forward contracts | Designated as Hedging Instrument | Other Assets
Asset Derivatives
Asset Derivatives	0	0
Foreign currency forward contracts | Designated as Hedging Instrument | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	0	93,996
Liability Derivatives
Liability Derivatives	5,574	320,873
Foreign currency forward contracts | Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	68,165	0
Foreign currency forward contracts | Not Designated as Hedging Instrument | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	0	32,339
Liability Derivatives
Liability Derivatives	0	0
Fuel contracts | Designated as Hedging Instrument | Other Assets
Asset Derivatives
Asset Derivatives	13,608	0
Fuel contracts | Designated as Hedging Instrument | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	0	0
Liability Derivatives
Liability Derivatives	129,486	307,475
Fuel contracts | Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	95,125	325,055
Fuel contracts | Not Designated as Hedging Instrument | Other Assets
Asset Derivatives
Asset Derivatives	543	0
Fuel contracts | Not Designated as Hedging Instrument | Derivative Financial Instruments
Asset Derivatives
Asset Derivatives	0	8,239
Liability Derivatives
Liability Derivatives	11,532	23,518
Fuel contracts | Not Designated as Hedging Instrument | Other long-term Liabilities
Liability Derivatives
Liability Derivatives	$ 5,936	$ 0