Organization and Basis of Presentation (Details 2)	6 Months Ended
	Jun. 30, 2011 SquareFoot
Real estate properties
Number of Properties	62
Square Feet (in square foot)	30,194,138
Weighted Average Occupancy (as a percent)	91.30%
Number of office properties managed	4
Rentable square feet of office properties	1,300,000
Number of shares to be received on redemption of one unit of limited partnership interests	1
Manhattan | Consolidated properties
Real estate properties
Number of Properties	24
Square Feet (in square foot)	17,197,945
Weighted Average Occupancy (as a percent)	92.80%
Manhattan | Unconsolidated properties
Real estate properties
Number of Properties	7
Square Feet (in square foot)	6,191,673
Weighted Average Occupancy (as a percent)	92.50%
Suburban | Consolidated properties
Real estate properties
Number of Properties	25
Square Feet (in square foot)	3,863,000
Weighted Average Occupancy (as a percent)	81.00%
Suburban | Unconsolidated properties
Real estate properties
Number of Properties	6
Square Feet (in square foot)	2,941,700
Weighted Average Occupancy (as a percent)	93.60%
Stand-alone retail properties
Real estate properties
Number of Properties	9
Square Feet (in square foot)	334,782
Development properties
Real estate properties
Number of Properties	6
Square Feet (in square foot)	1,359,941
Land interest
Real estate properties
Number of Properties	3