CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Increase (Decrease) in Prepaid Expense and Other Assets	$ (5,422,000)
Increase in accrued expenses, other liabilities and accrued interest payable	42,335,000
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Parent	(47,757,000)	$ (30,000)
Derivative Instruments, Loss Reclassified from Accumulated OCI into Income, Effective Portion	$ 1,374,000	$ 1,565,000
Supplemental disclosures of non-cash investing and financing activities
Stock issued in connection with stock grants (in shares)		154,645
Common stock issued through the dividend reinvestment plan (in shares)	576	484
Common stock issued through the dividend reinvestment plan	$ 101,000	$ 86,000
Number of shares withheld to satisfy employees' tax withholding and other liabilities	48,189	32,887
Shares withheld to satisfy employees' tax withholding and other liabilities, value	$ 8,164,000	$ 5,338,000
Stock Issued During Period, Shares, Share-based Compensation, Forfeited	12
Stock Issued During Period, Value, Share-based Compensation, Forfeited	$ 76,000
Net operating real estate	14,226,433,000
Dividends declared but not paid	185,173,000	165,241,000
(Decrease) increase in redeemable noncontrolling interests		2,065,000
Cash flow hedge losses reclassified to earnings	1,374,000	1,595,000
Impairment of Real Estate	(2,202,000)	$ 5,788,000
Cash in escrow	$ 170,361,000
Restricted Stock Converted From Performance Shares [Member]
Supplemental disclosures of non-cash investing and financing activities
Restricted stock granted	115,618	95,826
Restricted stock
Supplemental disclosures of non-cash investing and financing activities
Restricted stock granted	77,553	58,819
Fair value of shares issued	$ 12,529,000	$ 10,199,000
Stock Issued During Period, Shares, Share-based Compensation, Forfeited	499
Avalon at Edgewater [Member]
Supplemental disclosures of non-cash investing and financing activities
Net operating real estate	$ 21,844,000
Impairment of Real Estate	(8,702,000)	793,000
Insurance Proceeds In Escrow		22,000,000
New England [Member]
Supplemental disclosures of non-cash investing and financing activities
Impairment of Real Estate		$ 4,195,000
New England [Member] | Avalon at Edgewater [Member]
Supplemental disclosures of non-cash investing and financing activities
Impairment of Real Estate	$ 26,039,000