Derivative and Other Fair Value Instruments (Details Textuals) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Sep. 30, 2016
Derivative [Line Items]
Mortgage notes payable	$ 4,891,529	$ 4,891,529		$ 5,086,515
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)		(156,800)		(172,200)
Ineffective Portion - Amount of Gain/ (Loss) Reclassifed from Accumulated OCI into Income	(3,003)	(3,033)	$ 91
Secured Debt [Member]
Derivative [Line Items]
Mortgage notes payable	4,891,529	4,891,529		5,086,515
Debt Instrument, Fair Value Disclosure	4,900,000	4,900,000		5,100,000
Unsecured Debt [Member]
Derivative [Line Items]
Unsecured Debt	5,900,000	5,900,000		5,800,000
Debt Instrument, Fair Value Disclosure	$ 6,200,000	6,200,000		$ 6,100,000
3.375% Notes [Member] [Member]
Derivative [Line Items]
Payments for (Proceeds from) Hedge, Investing Activities		15,100
Proceeds from Issuance of Unsecured Debt		450,000
Ineffective Portion - Amount of Gain/ (Loss) Reclassifed from Accumulated OCI into Income		(30)
Interest Expense		1,200
ChargesHedgeTerminationActivities		$ 13,900
Scenario, Forecast [Member]
Derivative [Line Items]
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net					$ 24,200