Investment in Unconsolidated Joint Ventures (Details 2) (USD $)				1 Months Ended	12 Months Ended																																						1 Months Ended					1 Months Ended		1 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 1515 Broadway	Apr. 30, 2011 521 Fifth Avenue y	Dec. 31, 2011 521 Fifth Avenue	Dec. 31, 2011 Joint venture	Dec. 31, 2010 Joint venture	Dec. 31, 2009 Joint venture	Dec. 31, 2011 Joint venture 100 Park Avenue	Dec. 31, 2010 Joint venture 100 Park Avenue	Dec. 31, 2011 Joint venture 21 West 34th Street	Dec. 31, 2010 Joint venture 21 West 34th Street	Dec. 31, 2011 Joint venture 800 Third Avenue	Dec. 31, 2010 Joint venture 800 Third Avenue	Dec. 31, 2011 Joint venture One Court Square	Dec. 31, 2010 Joint venture One Court Square	Dec. 31, 2011 Joint venture 1604-1610 Broadway	Dec. 31, 2010 Joint venture 1604-1610 Broadway	Dec. 31, 2011 Joint venture 388 and 390 Greenwich Street	Dec. 31, 2010 Joint venture 388 and 390 Greenwich Street	Dec. 31, 2011 Joint venture 388 and 390 Greenwich Street Mortgage loan	Dec. 31, 2011 Joint venture 388 and 390 Greenwich Street Mezzanine loans	Dec. 31, 2011 Joint venture 1745 Broadway	Dec. 31, 2010 Joint venture 1745 Broadway	Dec. 31, 2011 Joint venture 141 Fifth Avenue	Dec. 31, 2010 Joint venture 141 Fifth Avenue	Dec. 31, 2011 Joint venture 1 and 2 Jericho Plaza	Dec. 31, 2010 Joint venture 1 and 2 Jericho Plaza	Dec. 31, 2011 Joint venture 11 West 34th Street	Dec. 31, 2010 Joint venture 11 West 34th Street	Dec. 31, 2011 Joint venture 280 Park Avenue	Dec. 31, 2010 Joint venture 1515 Broadway	Dec. 31, 2011 Joint venture The Meadows	Dec. 31, 2010 Joint venture The Meadows	Dec. 31, 2011 Joint venture 16 Court Street	Dec. 31, 2010 Joint venture 16 Court Street	Dec. 31, 2011 Joint venture 27-29 West 34th Street	Dec. 31, 2010 Joint venture 27-29 West 34th Street	Dec. 31, 2010 Joint venture 1551-1555 Broadway	Dec. 31, 2010 Joint venture 521 Fifth Avenue	Dec. 31, 2011 Joint venture 717 Fifth Avenue	Dec. 31, 2010 Joint venture 717 Fifth Avenue	May 31, 2011 Joint venture 379 West Broadway y	Dec. 31, 2011 Joint venture 379 West Broadway	Dec. 31, 2010 Joint venture 379 West Broadway	Dec. 31, 2011 Joint venture 600 Lexington Avenue	Dec. 31, 2010 Joint venture 600 Lexington Avenue	Dec. 31, 2010 Joint venture 180/182 Broadway and 63 Nassu Street	Dec. 31, 2011 Joint venture 180/182 Broadway and 63 Nassu Street	Apr. 30, 2011 Joint venture 3 Columbus Circle y	Dec. 31, 2011 Joint venture 3 Columbus Circle	Dec. 31, 2011 Joint venture 1552 Broadway	Dec. 31, 2011 Joint venture 747 Madison Avenue	Dec. 31, 2011 Joint venture Non Collateralized
First mortgage notes and other loan payable
Interest rate, fixed rate debt (as a percent)									6.64%	6.64%	5.76%	5.76%	6.00%	6.00%	4.91%	4.91%	5.66%	5.66%	5.19%	5.19%			5.68%	5.68%	5.70%	5.70%	5.65%	5.65%	4.82%	4.82%	6.57%
Interest rate, floating rate debt (as a percent)			3.50%		2.25%														1.43%	1.43%													1.63%	1.63%	2.75%	2.75%	1.90%	1.90%			5.25%	5.25%		1.94%	1.94%	2.38%	2.38%	3.00%	3.00%		2.47%	3.28%	3.02%	1.15%
Total fixed rate debt	$ 3,431,353,000	$ 2,935,817,000				$ 3,040,803,000	$ 2,321,364,000		$ 214,625,000	$ 204,946,000	$ 100,000,000	$ 100,000,000	$ 20,910,000	$ 20,910,000	$ 315,000,000	$ 315,000,000	$ 27,000,000	$ 27,000,000	$ 1,106,757,000	$ 1,106,758,000			$ 340,000,000	$ 340,000,000	$ 25,000,000	$ 25,000,000	$ 163,750,000	$ 163,750,000	$ 17,761,000	$ 18,000,000	$ 710,000,000
Other loan payable																																																						30,000,000
Total floating rate debt	942,487,000	464,651,000	450,363,000		150,000,000	1,091,087,000	1,390,871,000												31,622,000	31,622,000	16,000,000	15,600,000										462,896,000	84,698,000	87,034,000	85,728,000	86,844,000	53,900,000	54,375,000	128,600,000	140,000,000	245,000,000	245,000,000		20,991,000	20,991,000	125,000,000	125,000,000	8,509,000	30,722,000		254,896,000	95,405,000	33,125,000
Total mortgages and other loans payable	4,314,741,000	3,400,468,000				4,131,890,000	3,712,235,000														576,000,000	562,400,000
Committed amount																																	91,200,000								285,000,000								90,000,000			125,000,000
Maximum amount of loan recourse to entity						200,000,000																200,000,000
Mortgage repaid																																																31,000,000
Refinanced mortgage loan																																																		260,000,000
Portion of bridge loan provided to joint venture (as a percent)																																																		50.00%
Term of refinanced mortgage (in years)				2																																														5
Interest rate added to base rate (as a percent)					2.00%																																														2.10%
Interest rate, description				30-day LIBOR	30-Day LIBOR																																														30-day LIBOR
Possible increase in mortgage based on meeting certain performance hurdles																																																			40,000,000
Management, leasing, construction supervision and asset management services revenue						$ 12,100,000	$ 14,600,000	$ 19,000,000
Period for which the loan is extended (in years)																																											1