ACQUISITION AND DISPOSITION OF PROPERTIES, DISCONTINUED OPERATIONS AND PROPERTIES HELD FOR SALE - Acquisitions (Details) $ in Thousands		1 Months Ended									12 Months Ended
		Dec. 31, 2015 USD ($) ft² residential_unit	Nov. 30, 2015 USD ($) ft²	Oct. 31, 2015 USD ($) ft²	Sep. 30, 2015 USD ($) ft²	May. 31, 2015 USD ($) ft²		Apr. 30, 2015 USD ($) ft²	Mar. 31, 2015 USD ($) ft²	Jan. 31, 2015 USD ($) ft²	Dec. 31, 2015 USD ($) ft² residential_unit	May. 01, 2015	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
GLA (in square feet) | ft²		695,168									695,168
Core Portfolio [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²		305,800									305,800
Purchase Price											$ 204,200
Debt Assumption											9,800
Acquisition related costs											$ 1,300
Fund IV [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²		312,589									312,589
Purchase Price											$ 146,100
Debt Assumption											1,100
Acquisition related costs											$ 3,500
Fund II [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²		0									0
Purchase Price											$ 100,800
Debt Assumption											$ 81,000
City Center [Member] | San Francisco, California [Member] | Core Portfolio [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²									205,000
Percent Owned									100.00%
Purchase Price									$ 155,000
Debt Assumption									$ 0
163 Highland Avenue [Member] | Needham, MA [Member] | Core Portfolio [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²									40,500
Percent Owned									100.00%
Purchase Price									$ 24,000
Debt Assumption									$ 9,800
Route 202 Shopping Center [Member] | Wilmington, DE [Member] | Core Portfolio [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²	[1]							20,000
Percent Owned	[1]							100.00%
Purchase Price	[1]							$ 5,600
Debt Assumption	[1]							$ 0
Roosevelt Galleria [Member] | Chicago, Illinois [Member] | Core Portfolio [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²					40,300
Percent Owned					100.00%
Purchase Price					$ 19,600
Debt Assumption					$ 0
City Point Tower I [Member] | Fund II [Member]
Business Acquisition [Line Items]
Percent Owned		43.00%									43.00%
City Point Tower I [Member] | Brooklyn, New York [Member] | Fund II [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²	[2]					0
Percent Owned						95.00%	[2]					43.00%
Purchase Price	[2]					$ 100,800
Debt Assumption	[2]					$ 81,000
Business Combination, Step Acquisition, Equity Interest in Acquiree, Percentage								52.00%
Business Combination, Step Acquisition, Equity Interest in Acquiree, Including Subsequent Acquisition, Percentage						95.00%
Number of Units in Real Estate Property | residential_unit		250									250
1035 Third Avenue [Member] | New York, New York [Member] | Fund IV [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²	[3]									53,294
Percent Owned	[3]									100.00%
Purchase Price	[3]									$ 51,000
Debt Assumption	[3]									$ 0
801 Madison Avenue [Member] | New York, New York [Member] | Fund IV [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²								6,375
Percent Owned								100.00%
Purchase Price								$ 33,000
Debt Assumption								$ 0
650 Bald Hill Road [Member] | Warwick, Rhode Island [Member] | Fund IV [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²				225,000
Percent Owned				90.00%
Purchase Price				$ 9,200
Debt Assumption				$ 0
2208-2216 Filmore Street [Member] | San Francisco, California [Member] | Fund IV [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²				7,375
Percent Owned				90.00%
Purchase Price				$ 8,600
Debt Assumption				$ 0
146 Geary Street [Member] | San Francisco, California [Member] | Fund IV [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²			12,400
Percent Owned			100.00%
Purchase Price			$ 38,000
Debt Assumption			$ 0
2207 Fillmore Street [Member] | San Francisco, California [Member] | Fund IV [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²			3,870
Percent Owned			90.00%
Purchase Price			$ 2,800
Debt Assumption			$ 1,100
1861 Union Street [Member] | San Francisco, California [Member] | Fund IV [Member]
Business Acquisition [Line Items]
GLA (in square feet) | ft²		4,275									4,275
Percent Owned		90.00%									90.00%
Purchase Price		$ 3,500
Debt Assumption		0
Acquisitions In 2014 [Member]
Purchase Price Allocation
Land		137,120									$ 137,120		$ 149,609
Buildings and improvements		413,015									413,015		418,720
Acquisition-related intangible liabilities (in Acquired lease intangibles, net)		(29,064)									(29,064)		(6,434)
Acquisition-related intangible assets (in Acquired lease intangibles, net)		41,812									41,812		0
Above and below market debt assumed (included in Mortgages and other notes payable, net)		(3,088)									(3,088)		(2,100)
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Financial Liabilities											(988)
Total Consideration		559,795									559,795		$ 559,795
Adjustments
Land											(12,489)
Buildings and improvements											(5,705)
Acquisition-related intangible assets (in Acquired lease intangibles, net)											41,812
Acquisition-related intangible liabilities (in Acquired lease intangibles, net)											(22,630)
Above and below market debt assumed (included in Mortgages and other notes payable)											0
Acquisitions In 2015 [Member]
Purchase Price Allocation
Land		83,890									83,890
Buildings and improvements		258,926									258,926
Above and below market debt assumed (included in Mortgages and other notes payable, net)		(10,885)									(10,885)
Total Consideration		$ 331,931									$ 331,931
Route 202 Shopping Center [Member] | Core Portfolio [Member]
Business Acquisition [Line Items]
Percent Owned		77.78%						77.78%			77.78%

[1] Purchase price represents the 77.78% interest acquired from an unaffiliated third party.

[2] Fund II previously held a 52% interest in this unconsolidated affiliate. In connection with the disposition of Phase III of this project discussed below, Fund II acquired an additional 43% interest in Tower I of this development project, which is accounted for as an asset acquisition. In total, Fund II now owns 95% of this investment, which is a residential project anticipated to include 250 residential units.

[3] GLA includes a portion of office space and a below-grade operator controlled parking garage.