Mortgages and Other Loans Payable (Details) (USD $)	1 Months Ended				12 Months Ended					1 Months Ended																	1 Months Ended																							1 Months Ended	12 Months Ended					12 Months Ended
	Nov. 30, 2011	Sep. 30, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Other loan payable due June 2013	Dec. 31, 2010 Other loan payable due June 2013	Dec. 31, 2010 Other loan payable assigned to joint venture	Dec. 31, 2011 711 Third Avenue	Dec. 31, 2010 711 Third Avenue	Mar. 31, 2011 420 Lexington Avenue	Dec. 31, 2011 420 Lexington Avenue	Dec. 31, 2010 420 Lexington Avenue	Dec. 31, 2011 673 First Avenue	Dec. 31, 2010 673 First Avenue	Dec. 31, 2011 220 East 42nd Street	Dec. 31, 2010 220 East 42nd Street	Dec. 31, 2011 625 Madison Avenue	Dec. 31, 2010 625 Madison Avenue	Dec. 31, 2011 609 Fifth Avenue	Dec. 31, 2010 609 Fifth Avenue	Dec. 31, 2011 609 Partners, LLC	Dec. 31, 2010 609 Partners, LLC	Dec. 31, 2011 485 Lexington Avenue	Dec. 31, 2010 485 Lexington Avenue	Dec. 31, 2011 120 West 45th Street	Dec. 31, 2010 120 West 45th Street	Jun. 30, 2011 919 Third Avenue	Dec. 31, 2011 919 Third Avenue	Dec. 31, 2010 919 Third Avenue	Dec. 31, 2011 300 Main Street	Dec. 31, 2010 300 Main Street	Dec. 31, 2011 500 West Putnam Avenue	Dec. 31, 2010 500 West Putnam Avenue	Dec. 31, 2011 One Madison Avenue	Dec. 31, 2010 One Madison Avenue	Dec. 31, 2011 125 Park Avenue	Dec. 31, 2010 125 Park Avenue	Dec. 31, 2011 2 Herald Square	Dec. 31, 2010 2 Herald Square	Dec. 31, 2011 885 Third Avenue	Dec. 31, 2010 885 Third Avenue	Dec. 31, 2011 292 Madison Avenue	Dec. 31, 2010 292 Madison Avenue	Dec. 31, 2011 110 East 42nd Street	Dec. 31, 2011 Landmark Square	Dec. 31, 2010 Landmark Square	Dec. 31, 2011 Other loan payable due in September, 2019	Dec. 31, 2010 100 Church Street	Dec. 31, 2010 28 West 44th Street	Apr. 30, 2011 521 Fifth Avenue y	Dec. 31, 2011 521 Fifth Avenue	Dec. 31, 2011 1515 Broadway	Jan. 31, 2011 1515 Broadway	Dec. 31, 2011 180 Maiden Lane	Dec. 31, 2011 180 Maiden Lane SL Green Operating Partnership	Dec. 31, 2011 180 Maiden Lane SL Green Operating Partnership Series E preferred units
Mortgages and Other Loans Payable
Interest rate, fixed rate debt (as a percent)								4.99%			7.15%		5.67%		5.24%		7.22%		5.85%		5.00%		5.61%		6.12%		6.87%	5.12%		5.75%		5.52%		5.91%		5.75%		5.36%		6.26%		6.17%		5.81%	4.00%		8.00%
Interest rate, floating rate debt (as a percent)					3.47%																																														2.25%	3.50%		2.56%
Total fixed rate debt																																												$ 18,100,000
Total fixed rate debt			3,431,353,000	2,935,817,000				120,000,000	120,000,000		187,182,000	149,141,000	29,906,000	30,781,000	190,431,000	194,758,000	129,098,000	132,209,000	94,963,000	96,502,000	31,721,000	31,722,000	450,000,000	450,000,000	170,000,000	170,000,000		500,000,000	219,879,000	11,500,000	11,500,000	24,563,000	25,000,000	626,740,000	640,076,000	146,250,000	146,250,000	191,250,000	191,250,000	267,650,000	267,650,000	59,099,000	59,099,000	65,000,000	86,000,000		50,000,000
Other loan payable					62,792,000	62,792,000	30,000,000
Total floating rate debt			942,487,000	464,651,000																																										110,180,000		139,672,000	122,007,000		150,000,000	450,363,000		279,332,000
Total mortgages and other loans payable			4,373,840,000	3,400,468,000
Increase in loan amount										40,000,000
Controlling interest in the joint venture (as a percent)																												51.00%
Interest rate added to base rate (as a percent)					2.50%																																														2.00%
Interest rate, description					three month GBP LIBOR																																													30-day LIBOR	30-Day LIBOR
Refinanced mortgage loan																											500,000,000																							150,000,000
Mortgage on properties assumed																																																					140,000,000
Term (in years)																																																		2
Preferred units, shares issued	80,000																																																						63,900,000
Preferred Units (as a percent)	6.00%																																																							5.00%
Preferred units, liquidation preference (in dollars per share)	$ 25.00																																																						$ 1.00
Preferred units, shares redeemed																																																								32,200,000
Repaid loan		104,000,000																									219,900,000
Gross book value of the properties collateralizing the mortgages and other loans payable			$ 7,400,000,000	$ 5,800,000,000