Fair Value Measurements and Derivative Instruments (Income Statement Hedging Instruments) (Details) - Fair Value Hedging - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Effect of derivative instruments involved in fair value hedging on the consolidated financial statements
Amount of Gain (Loss) Recognized in Income on Derivative	$ 22,055	$ 54,747
Amount of Gain (Loss) Recognized in Income on Hedged Item	8,210	(16,901)
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	11,276	12,217
Amount of Gain (Loss) Recognized in Income on Hedged Item	15,743	17,403
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	10,779	42,530
Amount of Gain (Loss) Recognized in Income on Hedged Item	$ (7,533)	$ (34,304)