Derivative and Other Fair Value Instruments (Details Textuals) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Mortgage notes payable	$ 4,223,681	$ 4,685,134
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)	(126,000)	(151,800)
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	20,800
Mortgage notes payable, net
Derivative [Line Items]
Mortgage notes payable	4,200,000	4,700,000
Debt Instrument, Fair Value Disclosure	4,400,000	4,600,000
Unsecured Debt [Member]
Derivative [Line Items]
Unsecured Debt	4,400,000	6,200,000
Debt Instrument, Fair Value Disclosure	$ 4,700,000	$ 6,500,000