ACQUISITION AND DISPOSITION OF PROPERTIES, DISCONTINUED OPERATIONS AND PROPERTIES HELD FOR SALE Dispositions (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 sqft
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
GLA (in square feet)	510,219
Sales Price	$ 388,840,000
Gain/(Loss)	155,618,000
Walnut Hill Property [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Non-recourse debt	22,900,000
Lincoln Road Portfolio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain/(Loss)	102,900,000
Core Portfolio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
GLA (in square feet)	368,551
Core Portfolio [Member] | Walnut Hill Property [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
GLA (in square feet)	297,905	[1]
Sales Price	0	[1]
Gain/(Loss)	12,402,000	[1]
Core Portfolio [Member] | Land Sale [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
GLA (in square feet)	0
Sales Price	340,000
Gain/(Loss)	190,000
Fund III [Member] | Sheepshead Bay [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
GLA (in square feet)	96,418
Sales Price	20,200,000
Gain/(Loss)	1,399,000
Fund III [Member] | Lincoln Road Portfolio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
GLA (in square feet)	61,443	[2]
Sales Price	141,800,000	[2]
Gain/(Loss)	86,600,000	[2]
Fund II [Member] | City Point [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
GLA (in square feet)	0	[3]
Sales Price	26,300,000	[3]
Gain/(Loss)	561,000	[3]
Fund II [Member] | Other Post-sale Adjustments [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
GLA (in square feet)	0
Sales Price	0
Gain/(Loss)	(176,000)
Fund IV [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
GLA (in square feet)	472,551
Fund IV [Member] | Lincoln Road Portfolio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
GLA (in square feet)	54,453	[2]
Sales Price	200,200,000	[2]
Gain/(Loss)	$ 54,642,000	[2]

[1] This property was subject to $22.9 million of non-recourse debt and was foreclosed upon by the lender during March 2014, resulting in a $12.4 million gain.

[2] Both the Fund III and Fund IV Lincoln Road Portfolios were unconsolidated and as such, the Company's share of gains related to these sales, which aggregated $102.9 million, are included in gain on disposition of properties of unconsolidated affiliates in the 2014 Consolidated Statement of Income.

[3] Represents the sale of a portion of the residential air rights known as "Tower 2" associated with the Company's City Point development project.