ACQUISITION OF REAL ESTATE AND DISCONTINUED OPERATIONS Acquisitions (Details) (USD $) Share data in Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014		Dec. 31, 2013
Business Acquisition [Line Items]
Gross leasable area (in square feet)	510,219
Core Portfolio
Business Acquisition [Line Items]
Gross leasable area (in square feet)	161,032
Purchase Price	$ 243,709,000
Assumption of Debt	29,794,000
Acquisition costs	3,100,000
Fund IV
Business Acquisition [Line Items]
Gross leasable area (in square feet)	453,584
Purchase Price	59,225,000
Acquisition costs	3,000,000
11 E. Walton | Chicago, IL | Core Portfolio
Business Acquisition [Line Items]
Gross leasable area (in square feet)	6,738
Percent Owned	100.00%
Purchase Price	44,000,000
Assumption of Debt	0
61 Main Street | Westport, CT | Core Portfolio
Business Acquisition [Line Items]
Gross leasable area (in square feet)	3,400
Percent Owned	100.00%
Purchase Price	7,300,000
Assumption of Debt	0
865 W. North Avenue | Chicago, IL | Core Portfolio
Business Acquisition [Line Items]
Gross leasable area (in square feet)	16,000
Percent Owned	100.00%
Purchase Price	14,750,000
Assumption of Debt	0
252-256 Greenwich Avenue | Greenwich, CT | Core Portfolio
Business Acquisition [Line Items]
Gross leasable area (in square feet)	9,172
Percent Owned	100.00%
Purchase Price	24,450,000
Assumption of Debt	0
152-154 Spring Street | New York, NY | Core Portfolio
Business Acquisition [Line Items]
Gross leasable area (in square feet)	2,936
Percent Owned	90.00%
Purchase Price	38,000,000
Assumption of Debt	0
2520 Flatbush Avenue | Brooklyn, NY | Core Portfolio
Business Acquisition [Line Items]
Gross leasable area (in square feet)	29,114
Percent Owned	100.00%
Purchase Price	17,100,000
Assumption of Debt	0
Bedford Green | Bedford Hills, NY | Core Portfolio
Business Acquisition [Line Items]
Gross leasable area (in square feet)	90,472
Percent Owned	100.00%
Purchase Price	46,750,000
Assumption of Debt	29,794,000
131-135 Prince Street (1) | New York, NY | Core Portfolio
Business Acquisition [Line Items]
Gross leasable area (in square feet)	3,200
Percent Owned	100.00%
Purchase Price	51,359,000
Assumption of Debt	0
Broughton Street Portfolio | Savannah, GA | Fund IV
Business Acquisition [Line Items]
Gross leasable area (in square feet)	218,076	[1]
Percent Owned	50.00%	[1]
Purchase Price	33,856,000	[1]
Number of properties acquired	24
Number of properties acquired through asset acquisitions	9
Eden Square | Bear, DE | Fund IV
Business Acquisition [Line Items]
Gross leasable area (in square feet)	235,508	[2]
Percent Owned	90.00%	[2]
Purchase Price	25,369,000	[2]
Acquisitions In 2014
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net
Land	73,459,000
Buildings and improvements	220,375,000
Total consideration	293,834,000
Acquisitions in 2013
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net
Land	66,385,000		52,029,000
Buildings and improvements	144,617,000		173,605,000
Acquisition-related intangible assets (in Acquired lease intangibles, net)	19,574,000		0
Acquisition-related intangible liabilities (in Acquired lease intangibles, net)	(4,942,000)		0
Total consideration	225,634,000		225,634,000
Adjustments [Abstract]
Land	14,356,000
Buildings and improvements	(28,988,000)
Acquisition-related intangible assets (in Acquired lease intangibles, net)	19,574,000
Acquisition-related intangible liabilities (in Acquired lease intangibles, net)	(4,942,000)
Total consideration	$ 0
Common OP units
Business Acquisition [Line Items]
Shares issued in connection with the acquisition of a property (in shares)	1.4
Common OP units | 131-135 Prince Street (1)
Business Acquisition [Line Items]
Shares issued in connection with the acquisition of a property (in shares)	1.4

[1] The Broughton Street Portfolio consists of 24 properties. As the joint venture partner to these investments maintains operating control over the investments, these are accounted for under the equity method. Of the 24 properties, nine of them are accounted for as asset acquisitions as they were purchased vacant and require future development.

[2] As the joint venture partner to this investment maintains operating control over this investment, it is accounted for under the equity method.