Fair Value Measurements and Derivative Instruments (Details 8) (Fair Value Hedging, USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Effect of derivative instruments involved in fair value hedging on the consolidated financial statements
Amount of Gain (Loss) Recognized in Income on Derivative	$ 3,980	$ 754	$ (51,987)	$ 12,032
Amount of Gain (Loss) Recognized in Income on Hedged Item	8,883	21,195	83,655	33,660
Interest rate swaps | Interest expense, net of interest capitalized
Effect of derivative instruments involved in fair value hedging on the consolidated financial statements
Amount of Gain (Loss) Recognized in Income on Derivative	3,022	3,054	6,299	12,916
Amount of Gain (Loss) Recognized in Income on Hedged Item	9,503	8,634	28,102	23,001
Interest rate swaps | Other income (expense)
Effect of derivative instruments involved in fair value hedging on the consolidated financial statements
Amount of Gain (Loss) Recognized in Income on Derivative	958	(2,300)	(58,286)	(884)
Amount of Gain (Loss) Recognized in Income on Hedged Item	(620)	2,863	55,553	961
Interest rate swaps | Extinguishment of unsecured senior notes
Effect of derivative instruments involved in fair value hedging on the consolidated financial statements
Amount of Gain (Loss) Recognized in Income on Hedged Item		$ 9,698		$ 9,698