Mortgages and Other Loans Payable (Details) (USD $)	3 Months Ended			12 Months Ended					12 Months Ended			1 Months Ended																					1 Months Ended													12 Months Ended			1 Months Ended		1 Months Ended		1 Months Ended			1 Months Ended					1 Months Ended
	Dec. 31, 2012	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Other loan payable due June 2013	Dec. 31, 2011 Other loan payable due June 2013	Dec. 31, 2012 Master repurchase	Dec. 31, 2012 400 East 57th Street	Dec. 31, 2012 400 East 58th Street	Jun. 30, 2011 919 Third Avenue	Dec. 31, 2012 919 Third Avenue	Dec. 31, 2011 919 Third Avenue	Dec. 31, 2012 100 Church Street	Dec. 31, 2012 1 Madison Avenue	Dec. 31, 2011 1 Madison Avenue	Dec. 31, 2012 Other loan payable due in September, 2019	Dec. 31, 2011 Other loan payable due in September, 2019	Dec. 31, 2012 885 Third Avenue	Dec. 31, 2011 885 Third Avenue	Dec. 31, 2012 2 Herald Square	Dec. 31, 2011 2 Herald Square	Dec. 31, 2012 485 Lexington Avenue	Dec. 31, 2011 485 Lexington Avenue	Dec. 31, 2012 120 West 45th Street	Dec. 31, 2011 120 West 45th Street	Dec. 31, 2012 300 Main Street	Dec. 31, 2011 300 Main Street	Dec. 31, 2012 762 Madison Avenue	Dec. 31, 2012 Landmark Square	Dec. 31, 2011 Landmark Square	Mar. 31, 2011 420 Lexington Avenue	Dec. 31, 2012 420 Lexington Avenue	Dec. 31, 2011 420 Lexington Avenue	Dec. 31, 2012 500 West Putnam	Dec. 31, 2011 500 West Putnam	Dec. 31, 2012 625 Madison Avenue	Dec. 31, 2011 625 Madison Avenue	Dec. 31, 2012 711 Third Avenue	Dec. 31, 2011 711 Third Avenue	Dec. 31, 2012 125 Park Avenue	Dec. 31, 2011 125 Park Avenue	Dec. 31, 2012 609 Partners, LLC	Dec. 31, 2011 609 Partners, LLC	Dec. 31, 2012 609 Partners, LLC SL Green Operating Partnership Series E preferred units	Dec. 31, 2012 220 East 42nd Street	Dec. 31, 2011 220 East 42nd Street	Dec. 31, 2012 609 Fifth Avenue	Dec. 31, 2011 609 Fifth Avenue	Nov. 30, 2012 673 First Avenue	Dec. 31, 2011 673 First Avenue	Dec. 31, 2012 110 East 42nd Street	Dec. 31, 2011 110 East 42nd Street	Dec. 31, 2011 292 Madison Avenue	Apr. 30, 2012 1515 Broadway	Dec. 31, 2012 1515 Broadway	Dec. 31, 2011 1515 Broadway	Dec. 31, 2012 180 Maiden Lane	Dec. 31, 2011 180 Maiden Lane	Nov. 30, 2012 521 Fifth Avenue	Apr. 30, 2011 521 Fifth Avenue	Jan. 31, 2011 521 Fifth Avenue	Dec. 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%		5.36%		5.61%		6.12%		5.75%		3.75%	4.00%			7.50%		5.52%		7.22%		4.99%		5.75%		5.00%			5.25%		5.85%		5.67%			5.81%
Interest rate, floating rate debt (as a percent)									3.21%																																															3.60%	3.60%		2.42%
Total fixed rate debt																																																						$ 18,100,000
Total fixed rate debt	3,457,769,000			3,457,769,000	3,431,353,000					70,000,000	30,000,000		500,000,000	500,000,000	230,000,000	607,678,000	626,740,000	50,000,000	50,000,000	267,650,000	267,650,000	191,250,000	191,250,000	450,000,000	450,000,000	170,000,000	170,000,000	11,500,000	11,500,000	8,371,000	84,486,000	86,000,000		184,992,000	187,182,000	24,060,000	24,563,000	125,603,000	129,098,000	120,000,000	120,000,000	146,250,000	146,250,000	23,000	31,721,000		185,906,000	190,431,000		94,963,000		29,906,000		65,000,000	59,099,000
Total floating rate debt	1,157,695,000			1,157,695,000	942,487,000			62,792,000	116,667,000																																																769,813,000	450,363,000	271,215,000	279,332,000		150,000,000		150,000,000
Total mortgages and other loans payable	4,615,464,000			4,615,464,000	4,373,840,000
Interest in property (as a percent)													51.00%	51.00%																80.00%
Repaid loan												219,900,000																																									65,000,000			447,200,000
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
Ownership interest sold (as a percent)																																																													49.50%
Interest rate added to base rate (as a percent)							2.50%		3.00%																																															2.85%					2.20%	2.00%
Interest rate, description							three month GBP LIBOR		1-month LIBOR																																															90-day LIBOR						30-Day LIBOR
Mortgage on properties assumed																																																													170,000,000		140,000,000
Refinanced mortgage loan												500,000,000																																												775,000,000
Gross book value of the properties and debt and preferred equity investments collateralizing the mortgages and other loans payable	7,600,000,000			7,600,000,000	7,400,000,000
Term																																																								7 years					7 years	2 years
Extinguishment of debt																																																	93,300,000		29,100,000
(Gain) loss on early extinguishment of debt	6,978,000	67,000	(971,000)	6,978,000	(904,000)	1,900,000																																											3,100,000
Repurchase of debt									$ 175,000,000
Extension option available									1 year