Organization and Basis of Presentation (Details 2) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 sqft building		Dec. 31, 2012
Real estate properties
Number of buildings (buildings)	62
Square Feet (sqft)	28,549,979
Weighted Average Occupancy (as a percent)	92.50%	[1]
Debt and preferred equity investments	$ 1,304,839		$ 1,348,434
Number of shares to be received on redemption of one unit of limited partnership interests (shares)	1
Stand-alone retail properties
Real estate properties
Number of buildings (buildings)	16
Square Feet (sqft)	875,800
Development
Real estate properties
Number of buildings (buildings)	20
Square Feet (sqft)	3,230,800
Residential properties
Real estate properties
Number of buildings (buildings)	4
Square Feet (sqft)	719,900
Number of units (unit)	801
Land
Real estate properties
Square Feet (sqft)	961,400
Number of properties (properties)	2
Managed office properties
Real estate properties
Square Feet (sqft)	626,400
Number of office properties managed (property)	2
Manhattan | Consolidated properties
Real estate properties
Number of buildings (buildings)	23
Square Feet (sqft)	17,306,045
Weighted Average Occupancy (as a percent)	94.50%	[1]
Manhattan | Unconsolidated properties
Real estate properties
Number of buildings (buildings)	9
Square Feet (sqft)	5,934,434
Weighted Average Occupancy (as a percent)	96.60%	[1]
Suburban | Consolidated properties
Real estate properties
Number of buildings (buildings)	26
Square Feet (sqft)	4,087,400
Weighted Average Occupancy (as a percent)	79.80%	[1]
Suburban | Unconsolidated properties
Real estate properties
Number of buildings (buildings)	4
Square Feet (sqft)	1,222,100
Weighted Average Occupancy (as a percent)	87.20%	[1]
Southern California | Office properties
Real estate properties
Number of buildings (buildings)	52
Square Feet (sqft)	3,654,300
Number of properties (properties)	28

[1] The weighted average occupancy represents the total leased square feet divided by total available rentable square feet.