Derivative and Other Fair Value Instruments (Details Textuals) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Mortgage notes payable	$ 4,704,870,000	$ 5,086,515,000
Unrealized Gain (Loss) on Interest Rate Cash Flow Hedges, Pretax, Accumulated Other Comprehensive Income (Loss)	(151,800,000)	(172,200,000)
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	24,700,000
Payments for (Proceeds from) Hedge, Investing Activities		2,000,000	$ 44,700,000
Proceeds from Issuance of Unsecured Debt		750,000,000	500,000,000
Interest Expense		1,300,000	700,000
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	3,000,000	91,000	0
Charges Hedge Termination Activities		800,000	44,000,000
Secured Debt [Member]
Derivative [Line Items]
Mortgage notes payable	4,704,870,000	5,086,515,000
Debt Instrument, Fair Value Disclosure	4,600,000,000	5,100,000,000
Unsecured Debt [Member]
Derivative [Line Items]
Notes, net	6,300,000,000	5,800,000,000
Debt Instrument, Fair Value Disclosure	6,500,000,000	6,100,000,000
3.375% Notes [Member] [Member]
Derivative [Line Items]
Payments for (Proceeds from) Hedge, Investing Activities	15,100,000
Proceeds from Issuance of Unsecured Debt	450,000,000
Interest Expense	1,200,000
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	(30,000)
Charges Hedge Termination Activities	13,900,000
Forward Starting Swaps/Treasury Locks [Member]
Derivative [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net	$ (3,033,000)	$ 91,000	$ 0