Mortgages and Other Loans Payable (Details) (USD $)							3 Months Ended																																																																										3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 609 Partners, LLC		Dec. 31, 2013 609 Partners, LLC		Mar. 31, 2014 609 Partners, LLC Series E preferred units	Mar. 31, 2014 125 Park Avenue		Dec. 31, 2013 125 Park Avenue	Mar. 31, 2014 711 Third Avenue		Dec. 31, 2013 711 Third Avenue	Mar. 31, 2014 625 Madison Avenue		Dec. 31, 2013 625 Madison Avenue	Mar. 31, 2014 500 West Putnam		Dec. 31, 2013 500 West Putnam	Mar. 31, 2014 420 Lexington Avenue		Dec. 31, 2013 420 Lexington Avenue	Mar. 31, 2014 Landmark Square		Dec. 31, 2013 Landmark Square	Mar. 31, 2014 485 Lexington Avenue		Dec. 31, 2013 485 Lexington Avenue	Mar. 31, 2014 120 West 45th Street		Dec. 31, 2013 120 West 45th Street	Mar. 31, 2014 762 Madison Avenue		Dec. 31, 2013 762 Madison Avenue	Mar. 31, 2014 2 Herald Square		Dec. 31, 2013 2 Herald Square	Mar. 31, 2014 885 Third Avenue		Dec. 31, 2013 885 Third Avenue	Mar. 31, 2014 Other loan payable		Dec. 31, 2013 Other loan payable		Mar. 31, 2014 One Madison Avenue		Dec. 31, 2013 One Madison Avenue	Mar. 31, 2014 100 Church		Dec. 31, 2013 100 Church	Mar. 31, 2014 919 Third Avenue		Dec. 31, 2013 919 Third Avenue		Mar. 31, 2014 400 East 57th Street		Dec. 31, 2013 400 East 57th Street	Mar. 31, 2014 400 East 58th Street		Dec. 31, 2013 400 East 58th Street	Mar. 31, 2014 1515 Broadway		Dec. 31, 2013 1515 Broadway	Mar. 31, 2014 220 East 42nd Street		Dec. 31, 2013 220 East 42nd Street	Mar. 31, 2014 Master repurchase agreement		Dec. 31, 2013 Master repurchase agreement		Mar. 31, 2014 16 Court Street		Dec. 31, 2013 16 Court Street	Mar. 31, 2014 180 Maiden Lane		Dec. 31, 2013 180 Maiden Lane		Mar. 31, 2014 248-252 Bedford Avenue		Dec. 31, 2013 248-252 Bedford Avenue	Mar. 31, 2014 LIBOR Minimum Master repurchase agreement	Mar. 31, 2014 LIBOR Maximum Master repurchase agreement
Mortgages and Other Loans Payable
Interest rate, fixed rate debt (as a percent)			5.00%	[1],[2]				5.75%	[1]		4.99%	[1]		7.27%	[1]		5.52%	[1]		7.15%	[1]		4.00%	[1]		5.61%	[1]		6.12%	[1]		3.75%	[1]		5.36%	[1]		6.26%	[1]		8.00%	[1],[3]			5.91%	[1]		4.68%	[1]		5.12%	[1],[4]			4.13%	[1]		4.13%	[1]		3.93%	[1]
Interest rate, floating rate debt (as a percent)																																																																1.76%	[1]		3.37%	[1],[5]			4.00%	[1]		2.35%	[1],[6]			2.42%	[1]
Total fixed rate debt	$ 4,122,502,000	$ 4,130,629,000	$ 23,000	[2]	$ 23,000	[2]		$ 146,250,000		$ 146,250,000	$ 120,000,000		$ 120,000,000	$ 119,373,000		$ 120,830,000	$ 23,392,000		$ 23,529,000	$ 182,233,000		$ 182,641,000	$ 82,505,000		$ 82,909,000	$ 450,000,000		$ 450,000,000	$ 170,000,000		$ 170,000,000	$ 8,169,000		$ 8,211,000	$ 191,250,000		$ 191,250,000	$ 267,650,000		$ 267,650,000	$ 50,000,000	[3]	$ 50,000,000	[3]	$ 581,940,000		$ 587,336,000	$ 230,000,000		$ 230,000,000	$ 500,000,000	[4]	$ 500,000,000	[4]	$ 69,802,000		$ 70,000,000	$ 29,915,000		$ 30,000,000	$ 900,000,000		$ 900,000,000
Total floating rate debt	848,520,000	729,949,000																																																														275,000,000		275,000,000	212,216,000	[5]	91,000,000	[5]	78,768,000		79,243,000	260,536,000	[6]	262,706,000	[6]	22,000,000		22,000,000
Total mortgages and other loans payable	4,971,022,000	4,860,578,000
Preferred Units, shares issued (shares)							63,900,000
Preferred Units (as a percent)							5.00%
Preferred Units, liquidation preference (in dollars per share)							$ 1.00
Preferred Units, shares outstanding (shares)							22,658
Interest in property (as a percent)																																																			51.00%
Maximum borrowing capacity	300,000,000
Interest rate added to base rate (as a percent)																																																																																	2.50%	3.25%
Gross book value of the properties and debt and preferred equity investments collateralizing the mortgages and other loans payable	$ 8,000,000,000	$ 8,000,000,000

[1] Effective weighted average interest rate for the three months ended March 31, 2014, taking into account interest rate hedges in effect during the period.

[2] As part of an acquisition, the Operating Partnership issued 63.9 million units of its 5.0% Series E preferred units, or the Series E units, with a liquidation preference of $1.00 per unit. As of March 31, 2014, 22,658 Series E units remained outstanding. In April 2014, these Series E units were subsequently canceled.

[3] This loan is secured by a portion of a preferred equity investment.

[4] We own a 51.0% controlling interest in the joint venture that is the borrower on this loan.

[5] The Master Repurchase Agreement, as amended in December 2013, or MRA, provides us an ability to sell certain debt investments in exchange for cash with a simultaneous agreement to repurchase the same debt investments at a certain date or on demand. This MRA has a maximum facility capacity of $300.0 million and bears interest ranging from 250 and 325 basis points over one-month LIBOR depending on the pledged collateral.

[6] In connection with this consolidated joint venture obligation, we executed a master lease agreement. Our partner has executed a contribution agreement to reflect its pro rata share of the obligation under the master lease.