ACQUISITION AND DISPOSITION OF REAL ESTATE AND PROPERTIES HELD FOR SALE - Acquisition (Details) $ in Thousands	3 Months Ended
Mar. 31, 2016 USD ($) ft² shares	Dec. 31, 2015 USD ($)
Core Portfolio
Business Acquisition [Line Items]
Gross leasable area (in square feet) \| ft²	129,822
Purchase Price	$ 116,269
Assumption of Debt	10,472
Acquisition costs	$ 200
Fund IV
Business Acquisition [Line Items]
Gross leasable area (in square feet) \| ft²	19,528
Purchase Price	$ 13,750
Assumption of Debt	$ 1,463
Gotham Plaza \| New York, NY \| Core Portfolio
Business Acquisition [Line Items]
Gross leasable area (in square feet) \| ft²	122,902
Percentage of interests acquired	49.00%
Purchase Price	$ 39,808
Assumption of Debt	$ 10,472
991 Madison Avenue \| New York, NY \| Core Portfolio
Business Acquisition [Line Items]
Gross leasable area (in square feet) \| ft²	6,920
Percentage of interests acquired	100.00%
Purchase Price	$ 76,461
Assumption of Debt	$ 0
1964 Union Street \| San Francisco, CA \| Fund IV
Business Acquisition [Line Items]
Gross leasable area (in square feet) \| ft²	3,817
Percentage of interests acquired	90.00%
Purchase Price	$ 2,250
Assumption of Debt	$ 1,463
Restaurants at Fort Point \| Boston, MA \| Fund IV
Business Acquisition [Line Items]
Gross leasable area (in square feet) \| ft²	15,711
Percentage of interests acquired	100.00%
Purchase Price	$ 11,500
Assumption of Debt	$ 0
Acquisitions in 2015
Business Acquisition [Line Items]
Gross leasable area (in square feet) \| ft²	149,350
Purchase Price	$ 130,019
Assumption of Debt	11,935
Purchase Price Allocations
Land	67,017	$ 65,759
Buildings and improvements	192,472	204,532
Acquisition-related intangible assets (in Acquired lease intangibles, net)	20,326	0
Acquisition-related intangible liabilities (in Acquired lease intangibles, net)	(8,809)	0
Below market debt assumed (in Mortgage and other notes payable)	(10,480)	(9,765)
Total consideration	260,526	$ 260,526
Adjustments
Land	1,258
Buildings and improvements	(12,060)
Acquisition-related intangible assets (in Acquired lease intangibles, net)	20,326
Acquisition-related intangible liabilities (in Acquired lease intangibles, net)	(8,809)
Below market debt assumed (in Mortgage and other notes payable)	(715)
Total consideration	0
Acquisitions in 2016
Purchase Price Allocations
Land	23,192
Buildings and improvements	69,575
Debt assumed (included in Mortgage and other notes payable)	(21,371)
Total consideration	$ 71,396
Operating Partnership, as General Partner or Managing Member
Business Acquisition [Line Items]
Limited partners' capital account, units issued (in shares) \| shares	442,478
Series C Preferred Stock \| Operating Partnership, as General Partner or Managing Member
Business Acquisition [Line Items]
Limited partners' capital account, units issued (in shares) \| shares	141,593
Capital Lease Obligations \| 991 Madison Avenue
Business Acquisition [Line Items]
Lease term	49 years
Capital lease payments	$ 7,200

Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Buildings And Improvements

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Gross Leasable Area

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Percentage of voting equity interests acquired at the acquisition date in the business combination.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Amount of liabilities incurred by the acquirer as part of consideration transferred in a business combination.

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Amount of real estate acquired, at the acquisition date.

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Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.

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Amount of long-term debt due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of limited partner units issued.

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