Stockholders' Equity of the Company (Details) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended								9 Months Ended			1 Months Ended	9 Months Ended	1 Months Ended		9 Months Ended		1 Months Ended	9 Months Ended				9 Months Ended						9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Common Stock	Dec. 31, 2012 Common Stock	Sep. 30, 2013 Series I Preferred Units	Dec. 31, 2012 Series I Preferred Units	Sep. 30, 2013 Series C Preferred Units	Dec. 31, 2012 Series C Preferred Units	Sep. 30, 2013 SL Green Realty Corporation	Sep. 30, 2013 SL Green Realty Corporation Common Stock	Sep. 30, 2013 SL Green Realty Corporation At-the-market equity offering programs	Jul. 31, 2011 SL Green Realty Corporation At-the-market equity offering programs	Sep. 30, 2013 SL Green Realty Corporation Common Stock	Aug. 31, 2012 SL Green Realty Corporation Series I Preferred Units	Sep. 30, 2013 SL Green Realty Corporation Series I Preferred Units	Jun. 30, 2013 SL Green Realty Corporation Series C Preferred Units	Sep. 30, 2012 SL Green Realty Corporation Series C Preferred Units	Sep. 30, 2013 SL Green Realty Corporation Series C Preferred Units	Aug. 31, 2012 SL Green Realty Corporation Series C Preferred Units	Jul. 31, 2012 SL Green Realty Corporation Series D Preferred Stock [Member]	Sep. 30, 2013 SL Green Realty Corporation Series D Preferred Stock [Member]	Sep. 30, 2013 SL Green Realty Corporation Dividend Reinvestment and Stock Purchase Plan [Member]	Sep. 30, 2012 SL Green Realty Corporation Dividend Reinvestment and Stock Purchase Plan [Member]	Mar. 31, 2012 SL Green Realty Corporation Dividend Reinvestment and Stock Purchase Plan [Member]	Sep. 30, 2013 SL Green Operating Partnership	Sep. 30, 2012 SL Green Operating Partnership	Sep. 30, 2013 SL Green Operating Partnership Common Stock	Sep. 30, 2013 SL Green Operating Partnership Series I Preferred Units	Dec. 31, 2012 SL Green Operating Partnership Series I Preferred Units	Dec. 31, 2012 SL Green Operating Partnership Series C Preferred Units	Sep. 30, 2013 Stock Options Stock Appreciation Rights and Other Awards [Member]
Stockholders' Equity
Authorized capital stock (in shares)												260,000,000
Authorized shares, par value (in dollars per share)												$ 0.01
Common stock, shares authorized (in shares)	160,000,000		160,000,000		160,000,000							160,000,000															3,500,000
Common stock, par value (in dollars per share)	$ 0.01		$ 0.01		$ 0.01							$ 0.01
Common stock, shares issued (in shares)	95,780,000		95,780,000		94,896,000
Excess stock authorized (shares)												75,000,000
Excess stock, par value (in dollars per share)												$ 0.01
Preferred stock, shares authorized (shares)												25,000,000
Preferred stock, par value (in dollars per share)								$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01
Common stock, shares outstanding net of treasury shares (shares)						92,214,000	91,250,000						92,214,396
Excess Stock, Shares Issued																0
Value of shares to be issued (shares)															$ 250,000,000
Issuance of common stock (in shares)						462,000								462,276											651	1,300,000				462,276
Proceeds from Shares Sold Gross														42,500,000
Proceeds from Issuance of Common Stock			41,758,000	423,544,000										41,800,000											57,000	99,500,000		41,758,000	423,544,000
Aggregate value of shares available for issuance														2,800,000
Preferred stock, shares outstanding (in shares)								9,200,000	9,200,000		7,700,000							9,200,000				11,700,000									9,200,000	9,200,000	7,700,000
Preferred Units (as a percent)																		6.50%	7.625%				7.875%
Preferred stock, liquidation preference (in dollars per share)																		$ 25.00	$ 25.00	$ 25.00			$ 25.00
Perpetual Preferred stock, annual dividends per share (in dollars per share)																		$ 1.625			$ 1.90625			$ 1.96875
Net proceeds from sale of preferred stock																	221,900,000
Preferred units, outstanding																		9,200,000
Preferred Units, Dividend Rate, Percentage																		6.50%	7.625%				7.875%
Preferred stock redeemed (in shares)																			7,700,000	4,000,000			4,000,000
Amount of accumulated and unpaid dividends (in dollars per share)																			$ 0.3495	$ 0.3707			$ 0.4922
Preferred stock redemption costs	$ 0	$ 10,010,000	$ 12,160,000	$ 10,010,000															$ 12,200,000	$ 6,300,000			$ 3,700,000
Option expiration period																																		5 years