ACQUISITION AND DISPOSITION OF PROPERTIES AND DISCONTINUED OPERATIONS Acquisitions (Details) (USD $)								12 Months Ended													12 Months Ended									12 Months Ended
	Dec. 31, 2012 sqft	Dec. 31, 2012 Acquisitions in 2012 [Member] Purchase Price As Originally Reported [Member]	Dec. 31, 2012 Acquisitions in 2012 [Member] Finalized Purchase Price Allocation, Adjustment [Member]	Dec. 31, 2012 Acquisitions in 2012 [Member] Finalized Purchase Price Allocation [Member]	Dec. 31, 2012 Acquisitions in 2012 [Member] Preliminary Purchase Price Allocation [Member]	Dec. 31, 2011 Acquisitions in 2011 [Member] Finalized Purchase Price Allocation [Member]	Dec. 31, 2011 Acquisitions in 2011 [Member] Preliminary Purchase Price Allocation [Member]	Dec. 31, 2012 Core Portfolio [Member] sqft	Dec. 31, 2012 Core Portfolio [Member] 1520 North Milwaukee Avenue [Member] Chicago Illinois [Member] sqft	Dec. 31, 2012 Core Portfolio [Member] River Street [Member] Cambridge Massachusetts [Member] sqft	Dec. 31, 2012 Core Portfolio [Member] Chicago Street Retail Portfolio [Member] Chicago Illinois [Member] sqft	Dec. 31, 2012 Core Portfolio [Member] 930 Rush Street [Member] Chicago Illinois [Member] sqft	Dec. 31, 2012 Core Portfolio [Member] 28 Jericho Turnpike [Member] Westbury, New York [Member] sqft	Dec. 31, 2012 Core Portfolio [Member] Rhode Island Shopping Center [Member] Washington, D.C. [Member] sqft	Dec. 31, 2012 Core Portfolio [Member] 83 Spring Street [Member] New York New York [Member] sqft	Dec. 31, 2012 Core Portfolio [Member] 60 Orange Street [Member] Bloomfield, New Jersey [Member] sqft	Dec. 31, 2012 Core Portfolio [Member] Chicago Street Retail [Member] Chicago Illinois [Member] sqft	Dec. 31, 2012 Core Portfolio [Member] 181 Main Street [Member] West Port, Connecticut [Member] sqft	Dec. 31, 2012 Core Portfolio [Member] Connecticut Avenue [Member] Washington, D.C. [Member] sqft	Dec. 31, 2012 Core Portfolio [Member] 639 West Diversey [Member] Chicago Illinois [Member] sqft	Dec. 31, 2012 Fund III [Member] sqft	Feb. 29, 2012 Fund III [Member] 640 Broadway [Member] New York New York [Member] sqft	Apr. 30, 2012 Fund III [Member] Lincoln Park Centre LLC [Member] Chicago Illinois [Member] sqft	Aug. 31, 2012 Fund III [Member] Broad Hollow Commons [Member] Farmingdale, New York [Member]		Aug. 31, 2012 Fund III [Member] Arundel Plaza [Member] Glen Burnie, Maryland [Member] sqft	Aug. 31, 2012 Fund III [Member] Cortland Crossing [Member] Mohegan Lake, New York [Member]		Aug. 31, 2012 Fund III [Member] 3104 M Street [Member] Washington, D.C. [Member] sqft	Dec. 31, 2012 Fund IV [Member] sqft	Dec. 31, 2012 Fund IV [Member] One Seven Zero One Belmont Avenue [Member] Catonsville, Maryland [Member] sqft	Dec. 31, 2012 Fund IV [Member] 210 Bowery LLC [Member] Manhattan, New York [Member] sqft	Dec. 31, 2012 Fund IV [Member] Lincoln Road [Member] Miami, Florida [Member] sqft
Business Acquisition [Line Items]
GLA (in square feet)	398,874							509,843	3,100	53,300	42,264	2,900	96,000	57,000	4,800	129,010	42,524	14,850	42,000	22,095	378,300	45,700	62,700			265,000			4,900	121,600.00	58,000.00	9,200.00	54,400.00
Percent Owned									100.00%	100.00%	100.00%	100.00%	100.00%	100.00%	100.00%	98.00%	100.00%	100.00%	100.00%	100.00%		50.00%	100.00%	100.00%	[1],[2]	90.00%	100.00%	[1]	100.00%		90.00%	100.00%	95.00%
Purchase Price								$ 224,300,000	$ 3,800,000	$ 18,900,000	$ 18,800,000	$ 20,700,000	$ 27,300,000	$ 21,700,000	$ 11,500,000	$ 12,500,000	$ 41,100,000	$ 14,100,000	$ 23,200,000	$ 10,700,000	$ 107,986,000	$ 32,500,000	$ 31,500,000	$ 12,386,000	[1],[2]	$ 17,600,000	$ 11,000,000	[1]	$ 3,000,000	$ 151,200,000	$ 4,700,000	$ 7,500,000	$ 139,000,000
Liabilities Incurred								43,992,000	0	7,022,000	16,029,000	0	0	16,510,000	0	0	0	0	0	4,431,000	29,019,000	0	19,763,000	0	[1],[2]	9,256,000	0	[1]	0	0	0	0	0
Acquisition Related Costs								2,100,000													2,200,000									500,000
Business Acquisition, Purchase Price Allocation [Abstract]
Land		68,439,000	446,000	68,885,000	86,826,000	12,150,000	5,438,000
Buildings and Improvements		120,010,000	(2,083,000)	117,927,000	226,650,000	11,009,000	18,563,000
Acquisition-related intangible assets (in Acquired lease intangibles, net)		2,482,000	8,830,000	11,312,000	0	1,027,000	0
Acquisition-related intangible liabilities (in Acquired lease and other intangibles, net)		(4,387,000)	(7,267,000)	(11,654,000)	0	(185,000)	0
Above-below market debt assumed (included in Mortgages payable)		935,000	74,000	1,009,000	0
Total Consideration		$ 187,479,000	$ 0	$ 187,479,000	$ 313,476,000	$ 24,001,000	$ 24,001,000

[1] Acquisition of land which is not treated as a business combination in accordance with ASC Topic 805.

[2] Fund III obtained a deed in lieu of foreclosure on an undeveloped property encumbered by the Fund's $10.0 million first mortgage loan which originated in September 2008. The $12,386 includes the first mortgage loan along with accrued interest.