Fair Value Measurements and Derivative Instruments - Income Statement Hedging Instruments (Details) - Fair Value Hedging - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Effect of derivative instruments involved in hedging on the consolidated financial statements
Amount of Gain (Loss) Recognized in Income on Derivative	$ 55	$ (5,925)	$ 5,917	$ 34,667
Amount of Gain (Loss) Recognized in Income on Hedged Item	1,013	7,423	(841)	(17,675)
Interest rate swaps | Interest expense, net of interest capitalized
Effect of derivative instruments involved in hedging on the consolidated financial statements
Amount of Gain (Loss) Recognized in Income on Derivative	600	1,737	2,642	6,075
Amount of Gain (Loss) Recognized in Income on Hedged Item	0	0	0	7,203
Interest rate swaps | Other income (expense)
Effect of derivative instruments involved in hedging on the consolidated financial statements
Amount of Gain (Loss) Recognized in Income on Derivative	(545)	(7,662)	3,275	28,592
Amount of Gain (Loss) Recognized in Income on Hedged Item	$ 1,013	$ 7,423	$ (841)	$ (24,878)