Investments in Real Estate Entities (Details 2)	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($) agreement	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) agreement	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Assets:
Real estate, net	$ 1,390,002,000		$ 1,390,002,000		$ 1,617,627,000
Other assets	180,919,000		180,919,000		72,290,000
Total assets	1,570,921,000		1,570,921,000		1,689,917,000
Liabilities and partners' capital:
Mortgage notes payable and credit facility	902,242,000		902,242,000		980,128,000
Other liabilities	23,891,000		23,891,000		24,884,000
Partners' capital	644,788,000		644,788,000		684,905,000
Total liabilities and partners' capital	1,570,921,000		1,570,921,000		1,689,917,000
Combined summary of the operating results of the accounted for using the equity method
Rental and other income	43,868,000	$ 49,388,000	132,518,000	$ 154,034,000
Operating and other expenses	(17,910,000)	(19,989,000)	(52,622,000)	(61,680,000)
Gain on sale of communities	66,410,000	327,539,000	98,899,000	333,221,000
Interest expense, net	(14,883,000)	(22,922,000)	(35,694,000)	(50,335,000)
Depreciation expense	(11,213,000)	(11,934,000)	(35,058,000)	(40,214,000)
Net income	66,272,000	322,082,000	108,043,000	335,026,000
Equity in income of unconsolidated real estate entities	20,554,000	130,592,000	68,925,000	143,527,000
Expensed acquisition, development and other pursuit costs, net of recoveries	3,391,000	406,000	5,251,000	3,139,000
Impairment of Real Estate	658,000	0	(10,668,000)	0
Other than Temporary Impairment Losses, Investments	0	$ 0	0	$ 0
Real Estate Investment Property, Net	13,694,690,000		13,694,690,000		13,219,140,000
Fund II
Combined summary of the operating results of the accounted for using the equity method
Costs in excess of equity in underlying net assets of the respective investments	$ 2,591,000		$ 2,591,000		$ 3,880,000
Guarantor Obligations, Liquidation Proceeds, Percentage			10.00%
Residual Joint Venture [Member]
Combined summary of the operating results of the accounted for using the equity method
Number of Limited Liability Company Agreements | agreement	3		3
Equity in income of unconsolidated real estate entities			$ 11,630,000
Sheepshead Bay [Member]
Combined summary of the operating results of the accounted for using the equity method
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage			70.00%
Variable Interest Entity, Ownership Interest by Partner			30.00%
Due from Related Parties	$ 7,340,000		$ 7,340,000
Avalon Mills [Member]
Combined summary of the operating results of the accounted for using the equity method
Impairment of Real Estate			800,000
Avalon at Edgewater [Member]
Combined summary of the operating results of the accounted for using the equity method
Impairment of Real Estate	658,000		(15,663,000)
Insurance Proceeds			44,142,000
Real Estate Investment Property, Net	$ 21,844,000		21,844,000
Casualty Loss			6,635,000
New England [Member]
Combined summary of the operating results of the accounted for using the equity method
Impairment of Real Estate			$ 4,195,000
Residual Joint Venture [Member]
Combined summary of the operating results of the accounted for using the equity method
Ownership Interest Held by Subsidiaries	40.00%		40.00%