Mortgages and Other Loans Payable (Details) (USD $)			3 Months Ended				1 Months Ended																							1 Months Ended													9 Months Ended								1 Months Ended	3 Months Ended				1 Months Ended	3 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Other loan payable due June 2013	Dec. 31, 2011 Other loan payable due June 2013	Sep. 30, 2012 400 East 57th Street	Sep. 30, 2012 400 East 58th Street	Jun. 30, 2011 919 Third Avenue	Sep. 30, 2012 919 Third Avenue	Dec. 31, 2011 919 Third Avenue	Sep. 30, 2012 100 Church Street	Sep. 30, 2012 One Madison Avenue	Dec. 31, 2011 One Madison Avenue	Sep. 30, 2012 Other loan payable due in September, 2019	Dec. 31, 2011 Other loan payable due in September, 2019	Sep. 30, 2012 885 Third Avenue	Dec. 31, 2011 885 Third Avenue	Sep. 30, 2012 110 East 42nd Street	Dec. 31, 2011 110 East 42nd Street	Sep. 30, 2012 2 Herald Square	Dec. 31, 2011 2 Herald Square	Sep. 30, 2012 485 Lexington Avenue	Dec. 31, 2011 485 Lexington Avenue	Sep. 30, 2012 120 West 45th Street	Dec. 31, 2011 120 West 45th Street	Sep. 30, 2012 300 Main Street	Dec. 31, 2011 300 Main Street	Sep. 30, 2012 762 Madison Avenue	Sep. 30, 2012 Landmark Square	Dec. 31, 2011 Landmark Square	Mar. 31, 2011 420 Lexington Avenue	Sep. 30, 2012 420 Lexington Avenue	Dec. 31, 2011 420 Lexington Avenue	Sep. 30, 2012 500 West Putnam	Dec. 31, 2011 500 West Putnam	Sep. 30, 2012 625 Madison Avenue	Dec. 31, 2011 625 Madison Avenue	Sep. 30, 2012 711 Third Avenue	Dec. 31, 2011 711 Third Avenue	Sep. 30, 2012 125 Park Avenue	Dec. 31, 2011 125 Park Avenue	Sep. 30, 2012 609 Partners, LLC	Dec. 31, 2011 609 Partners, LLC	Sep. 30, 2012 609 Partners, LLC SL Green Operating Partnership Series E preferred units	Sep. 30, 2012 220 East 42nd Street	Dec. 31, 2011 220 East 42nd Street	Sep. 30, 2012 609 Fifth Avenue	Dec. 31, 2011 609 Fifth Avenue	Sep. 30, 2012 673 First Avenue	Dec. 31, 2011 673 First Avenue	Dec. 31, 2011 292 Madison Avenue	Apr. 30, 2012 1515 Broadway	Sep. 30, 2012 1515 Broadway	Dec. 31, 2011 1515 Broadway	Sep. 30, 2012 180 Maiden Lane	Dec. 31, 2011 180 Maiden Lane	Apr. 30, 2011 521 Fifth Avenue	Sep. 30, 2011 521 Fifth Avenue	Sep. 30, 2012 521 Fifth Avenue	Dec. 31, 2011 521 Fifth Avenue	Jan. 31, 2011 521 Fifth Avenue
Mortgages and Other Loans Payable
Interest rate, fixed rate debt (as a percent)					4.13%	4.13%	6.87%	5.12%		4.68%	5.91%		8.00%		6.26%		5.81%		5.36%		5.61%		6.12%		5.75%		3.75%	4.00%			7.15%		5.52%		7.22%		4.99%		5.75%		5.00%			5.25%		5.85%		5.67%			3.60%
Interest rate, floating rate debt (as a percent)			3.35%																																																	3.52%		2.56%				2.24%
Total fixed rate debt																		$ 18,100,000
Total fixed rate debt	3,654,167,000	3,431,353,000			70,000,000	30,000,000		500,000,000	500,000,000	230,000,000	612,600,000	626,740,000	50,000,000	50,000,000	267,650,000	267,650,000	65,000,000	65,000,000	191,250,000	191,250,000	450,000,000	450,000,000	170,000,000	170,000,000	11,500,000	11,500,000	8,410,000	84,870,000	86,000,000		185,739,000	187,182,000	24,189,000	24,563,000	126,624,000	129,098,000	120,000,000	120,000,000	146,250,000	146,250,000	23,000	31,721,000		187,072,000	190,431,000	93,768,000	94,963,000	29,222,000	29,906,000	59,099,000
Total floating rate debt	1,257,858,000	942,487,000	62,792,000	62,792,000																																																771,786,000	450,363,000	273,280,000	279,332,000			150,000,000	150,000,000
Total mortgages and other loans payable	4,912,025,000	4,373,840,000
Controlling interest in the joint venture (as a percent)									51.00%
Repaid loan							219,900,000																																												447,200,000						140,000,000
Increase in loan amount																														40,000,000
Preferred Units, shares issued																																											63,900,000
Preferred Units (as a percent)																																											5.00%
Preferred Units, liquidation preference (in dollars per share)																																											$ 1.00
Preferred units, shares redeemed																																											63,800,000
Interest rate added to base rate (as a percent)			2.50%																																																2.85%					2.00%
Interest rate, description			three month GBP LIBOR																																																	90-Day LIBOR				30-Day LIBOR
Refinanced mortgage loan							500,000,000																																												775,000,000					150,000,000
Mortgage on properties assumed																																																												140,000,000
Gross book value of the properties collateralizing the mortgages and other loans payable	$ 7,600,000,000	$ 7,400,000,000
Term																																																			7 years					2 years