Mortgages and Other Loans Payable (Details) (USD $)	3 Months Ended		6 Months Ended			6 Months Ended																																										6 Months Ended																																					6 Months Ended							1 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Jun. 30, 2014 Series J Preferred Units		Dec. 31, 2013 Series J Preferred Units		Jun. 30, 2014 Master repurchase agreement		Dec. 31, 2013 Master repurchase agreement		Jun. 30, 2014 125 Park Avenue		Dec. 31, 2013 125 Park Avenue	Jun. 30, 2014 711 Third Avenue		Dec. 31, 2013 711 Third Avenue	Jun. 30, 2014 625 Madison Avenue		Dec. 31, 2013 625 Madison Avenue	Jun. 30, 2014 500 West Putnam Avenue		Dec. 31, 2013 500 West Putnam Avenue	Jun. 30, 2014 420 Lexington Avenue		Dec. 31, 2013 420 Lexington Avenue	Jun. 30, 2014 Landmark Square		Dec. 31, 2013 Landmark Square	Jun. 30, 2014 485 Lexington Avenue		Dec. 31, 2013 485 Lexington Avenue	Jun. 30, 2014 120 West 45th Street		Dec. 31, 2013 120 West 45th Street	Jun. 30, 2014 762 Madison Avenue		Dec. 31, 2013 762 Madison Avenue	Jun. 30, 2014 2 Herald Square		Dec. 31, 2013 2 Herald Square		Jun. 30, 2014 885 Third Avenue		Dec. 31, 2013 885 Third Avenue	Jun. 30, 2014 388 and 390 Greenwich Street		Dec. 31, 2013 388 and 390 Greenwich Street		Jun. 30, 2014 Other loan payable		Dec. 31, 2013 Other loan payable		Jun. 30, 2014 One Madison Avenue		Dec. 31, 2013 One Madison Avenue	Jun. 30, 2014 100 Church		Dec. 31, 2013 100 Church	Jun. 30, 2014 919 Third Avenue		Dec. 31, 2013 919 Third Avenue		Jun. 30, 2014 400 East 57th Street		Dec. 31, 2013 400 East 57th Street	Jun. 30, 2014 400 East 58th Street		Dec. 31, 2013 400 East 58th Street	Jun. 30, 2014 1515 Broadway		Dec. 31, 2013 1515 Broadway	Jun. 30, 2014 609 Partners, LLC		Dec. 31, 2013 609 Partners, LLC		Jun. 30, 2014 609 Partners, LLC Series E preferred units	Jun. 30, 2014 Master repurchase agreement	Jun. 30, 2014 180 Maiden Lane		Dec. 31, 2013 180 Maiden Lane		Jun. 30, 2014 248-252 Bedford Avenue		Dec. 31, 2013 248-252 Bedford Avenue		Jun. 30, 2014 220 East 42nd Street		Dec. 31, 2013 220 East 42nd Street	Apr. 30, 2014 16 Court Street	Jun. 30, 2014 16 Court Street		Dec. 31, 2013 16 Court Street
Mortgages and Other Loans Payable
Interest rate, fixed rate debt (as a percent)						3.75%	[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],[3]			6.26%	[1]		3.80%	[1],[4]			8.00%	[1],[5]			5.91%	[1]		4.68%	[1]		5.12%	[1],[6]			4.13%	[1]		4.13%	[1]		3.93%	[1]		0.00%	[1],[7]
Total fixed rate debt	$ 4,622,075,000		$ 4,622,075,000		$ 4,130,629,000	$ 4,000,000	[2]	$ 0	[2]					$ 146,250,000		$ 146,250,000	$ 120,000,000		$ 120,000,000	$ 117,892,000		$ 120,830,000	$ 23,253,000		$ 23,529,000	$ 181,612,000		$ 182,641,000	$ 82,097,000		$ 82,909,000	$ 450,000,000		$ 450,000,000	$ 170,000,000		$ 170,000,000	$ 8,128,000		$ 8,211,000	$ 191,250,000	[3]	$ 191,250,000	[3]	$ 267,650,000		$ 267,650,000	$ 504,000,000	[4]	$ 0	[4]	$ 50,000,000	[5]	$ 50,000,000	[5]	$ 576,653,000		$ 587,336,000	$ 230,000,000		$ 230,000,000	$ 500,000,000	[6]	$ 500,000,000	[6]	$ 69,503,000		$ 70,000,000	$ 29,787,000		$ 30,000,000	$ 900,000,000		$ 900,000,000	$ 0	[7]	$ 23,000	[7]
Interest rate, floating rate debt (as a percent)										3.37%	[1],[8]																																					1.91%	[1],[4]																																2.34%	[1],[9]			2.16%	[1],[10]			1.76%	[1]
Total floating rate debt	1,508,351,000		1,508,351,000		729,949,000					0	[8]	91,000,000	[8]																																			946,000,000	[4]	0	[4]																														258,351,000	[9]	262,706,000	[9]	29,000,000	[10]	22,000,000	[10]	275,000,000		275,000,000		0	[11]	79,243,000	[11]
Mortgages and other loans payable	6,130,426,000		6,130,426,000		4,860,578,000
Liabilities related to assets held for sale	193,375,000		193,375,000		0																																				191,300,000
Debt refinanced																																																1,100,000,000
Face amount of loan																																																1,500,000,000																																					29,000,000
Term																																																7 years																																					5 years
Interest in property (as a percent)																																																														51.00%
Limited partner interests in Operating Partnership, limited partner common units outstanding (shares)						4,000,000
Dividend rate preferred units (as a percent)						3.75%
Preferred stock, liquidation preference (in dollars per share)						$ 1,000.00
Preferred Units, shares outstanding (shares)						4,000																																																																									22,658
Maximum borrowing capacity																																																																																300,000,000
Loss on early extinguishment of debt	1,028,000	10,000	1,025,000	18,523,000																																																																																	500,000							500,000
Gross book value of the properties and debt and preferred equity investments collateralizing the mortgages and other loans payable	$ 9,500,000,000		$ 9,500,000,000		$ 8,000,000,000

[1] Effective weighted average interest rate for the three months ended June 30, 2014, taking into account interest rate hedges in effect during the period.

[2] In connection with the subsequent acquisition of a commercial real estate property, the Operating Partnership issued $4.0 million or 4,000 3.75% Series J Preferred Units of limited partnership interest, of the Series J Preferred Units, with a mandatory liquidation preference of $1,000.00 per unit. The Series J Preferred Units can be redeemed in cash by the Operating Partnership on the earlier of (i) the date of the sale of the property or (ii) April 30, 2051 or at the option of the unitholders as further prescribed in the related agreement.

[3] This property is held for sale at June 30, 2014 and the related $191.3 million mortgage is included in liabilities related to assets held for sale.

[4] Simultaneous with the acquisition of our joint venture partner interest, we refinanced the $1.1 billion floating rate mortgage with a $1.5 billion seven-year floating rate mortgage, and have consolidated the property.

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

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

[7] In April 2014, the remaining 22,658 Series E Preferred Units of the Operating Partnership were canceled.

[8] The Master Repurchase Agreement, or MRA, has a maximum facility capacity of $300.0 million.

[9] 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

[10] In June 2014, we replaced the previous floating rate mortgage with a $29.0 million, five-year floating rate mortgage and incurred a net loss on early extinguishment of debt of $0.5 million.

[11] In April 2014, we repaid the loan and incurred a loss on early extinguishment of debt of $0.5 million.