ACQUISITION AND DISPOSITION OF REAL ESTATE AND PROPERTIES HELD FOR SALE - Dispositions (Details) - Jun. 30, 2015 $ in Thousands	USD ($) ft²
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross leasable area (in square feet) | ft²	337,427
Sale Price	$ 300,350
Gain on Sale	$ 106,089
Lincoln Park Centre
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross leasable area (in square feet) | ft²	61,761
Sale Price	$ 64,000
Gain on Sale	$ 27,143
White City
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross leasable area (in square feet) | ft²	249,549
Sale Price	$ 96,750
Gain on Sale	$ 17,105
City Point
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross leasable area (in square feet) | ft²	0
Sale Price	$ 115,600
Gain on Sale	$ 49,884
Liberty Avenue
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gross leasable area (in square feet) | ft²	26,117
Sale Price	$ 24,000
Gain on Sale	$ 11,957