ACQUISITION OF REAL ESTATE AND DISCONTINUED OPERATIONS Acquisitions (Details) (USD $)	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Gross leasable area	394,323
Core Portfolio
Business Acquisition [Line Items]
Gross leasable area	67,360
Purchase Price	$ 145,700,000
Acquisition costs	1,500,000
Fund IV
Business Acquisition [Line Items]
Gross leasable area	157,383
Purchase Price	26,000,000
Acquisition costs	2,500,000
11 E Walton | Chicago, IL | Core Portfolio
Business Acquisition [Line Items]
Gross leasable area	6,738
Percent Owned	100.00%
Purchase Price	44,000,000
61 Main Street | Westport, CT | Core Portfolio
Business Acquisition [Line Items]
Gross leasable area	3,400
Percent Owned	100.00%
Purchase Price	7,300,000
865 W North Avenue | Chicago, IL | Core Portfolio
Business Acquisition [Line Items]
Gross leasable area	16,000
Percent Owned	100.00%
Purchase Price	14,800,000
252-256 Greenwich Avenue | Greenwich, CT | Core Portfolio
Business Acquisition [Line Items]
Gross leasable area	9,172
Percent Owned	100.00%
Purchase Price	24,500,000
152-154 Spring Street | New York, NY | Core Portfolio
Business Acquisition [Line Items]
Gross leasable area	2,936
Percent Owned	90.00%
Purchase Price	38,000,000
2520 Flatbush Avenue | Brooklyn, NY | Core Portfolio
Business Acquisition [Line Items]
Gross leasable area	29,114
Percent Owned	100.00%
Purchase Price	17,100,000
Broughton Street Portfolio (18 Properties) | Savannah, GA | Fund IV
Business Acquisition [Line Items]
Gross leasable area	157,383
Percent Owned	50.00%
Purchase Price	26,000,000
Number of properties acquired	18,000
Acquisitions In 2014
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net
Land	44,027,000
Buildings and improvements	127,579,000
Total consideration	171,606,000
Acquisitions in 2013
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net
Land	49,936,000	41,700,000
Buildings and improvements	121,978,000	142,618,000
Acquisition-related intangible assets (in Acquired lease intangibles, net)	15,716,000	0
Acquisition-related intangible liabilities (in Acquired lease intangibles, net)	(3,312,000)	0
Total consideration	184,318,000	184,318,000
Adjustments [Abstract]
Land	8,236,000
Buildings and improvements	(20,640,000)
Acquisition-related intangible assets (in Acquired lease intangibles, net)	15,716,000
Acquisition-related intangible liabilities (in Acquired lease intangibles, net)	(3,312,000)
Total consideration	$ 0