Property Acquisitions (Details) (USD $)			1 Months Ended				1 Months Ended			0 Months Ended
	Jun. 30, 2013 sqft	Dec. 31, 2012	Apr. 30, 2013 16 Court Street sqft	Mar. 31, 2013 248-252 Bedford Avenue item	Dec. 31, 2012 131-137 Spring Street sqft	Dec. 31, 2012 985-987 Third Avenue sqft	Oct. 31, 2012 1080 Amsterdam Avenue item sqft	Sep. 30, 2012 635 and 641 Sixth Avenue sqft	Jun. 30, 2012 304 Park Avenue South sqft	Jan. 31, 2012 Manhattan Series G preferred units	Jan. 31, 2012 Retail properties item	Jan. 31, 2012 Multifamily properties item sqft	Jan. 31, 2012 Stonehenge Properties
Property Acquisitions
Floating interest rate mortgage loan	$ 505,753,000	$ 1,157,695,000		$ 22,000,000
Interest rate, basis points (as a percent)				2.25%
Interest rate, description				LIBOR
Number of apartment units acquired				72
Number of townhouses acquired				12
Number of units				84			96					385
Purchase consideration				21,782,000	122,300,000			173,000,000	135,000,000				78,121,000
Area of property (in square feet)	29,721,879		318,000		68,000	42,000	82,250	267,000	215,000			488,000
Consolidated interest in acquiree			96,200,000
Purchase price fair value adjustment recognized			(2,300,000)
Term of lease							99 years
Consideration in cash									102,000,000
Value of operating partnership units issued									33,000,000	47,600,000
Number of properties acquired											5	2
Stated interest rate of preferred partnership units issued (as a percent)										4.50%
Term				5 years							5 years	12 years
Fixed rate debt	4,340,978,000	3,457,769,000									8,500,000	100,000,000
Interest rate, fixed rate debt (as a percent)											3.75%	4.125%
Number of properties with new mortgage											1
Ownership interest in consolidated joint venture (as a percent)				90.00%									80.00%
Allocation of the purchase price of the assets acquired and liabilities assumed
Land				10,865,000	27,021,000			69,848,000	54,189,000				65,533,000
Building and building leasehold				44,035,000	105,342,000			104,474,000	75,619,000				128,457,000
Above market lease value					179,000				2,824,000				594,000
Acquired in-place leases					7,046,000			7,727,000	8,265,000				9,573,000
Other assets, net of other liabilities													2,190,000
Assets acquired				54,900,000	139,588,000			182,049,000	140,897,000				206,347,000
Below market lease value					17,288,000			9,049,000	5,897,000				13,239,000
Liabilities assumed					17,288,000			9,049,000	5,897,000				13,239,000
Purchase price allocation			4,000,000	54,900,000	122,300,000	18,000,000		173,000,000	135,000,000				193,108,000
Net consideration funded by us at closing excluding consideration financed by debt				21,782,000	122,300,000			173,000,000	135,000,000				78,121,000
Debt assumed			$ 84,700,000