Capital (Details) (USD $)	3 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended		1 Months Ended			12 Months Ended			12 Months Ended
	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Aug. 31, 2012 Series I Preferred Units	Dec. 31, 2012 Series I Preferred Units	Sep. 30, 2012 Series C preferred units	Dec. 31, 2012 Series C preferred units	Jul. 31, 2012 Series D preferred units	Dec. 31, 2012 Series D preferred units	Dec. 31, 2012 Series E preferred units	Nov. 30, 2011 Series H Preferred Units	Jan. 31, 2012 Series G Preferred Units	Dec. 31, 2012 Series F Preferred Units	Dec. 31, 2012 At-the-market equity offering program	Jul. 31, 2011 At-the-market equity offering program	Dec. 31, 2012 SL Green	Dec. 31, 2012 SL Green Dividend Reinvestment and Stock Purchase Plan (DRIP)	Dec. 31, 2011 SL Green Dividend Reinvestment and Stock Purchase Plan (DRIP)	Mar. 31, 2012 SL Green Dividend Reinvestment and Stock Purchase Plan (DRIP)
Capital
Number of common units held by parent																	91,249,632
Period for which redemption right of unitholder is restricted		1 year
Number of shares to be received on redemption of one unit of limited partnership interests		1
Aggregate value of the shares of common stock to be sold																$ 250,000,000
Aggregate gross proceeds from shares sold															204,600,000
Proceeds from shares sold		201,279,000	516,168,000												201,300,000			99,600,000	34,000
Amount contributed															201,300,000			99,600,000
Number of common partnership units exchanged (in shares)															2,600,000			1,300,000	473
Aggregate value of shares available for issuance															45,400,000
Limited partnership interest held by noncontrolling investors (as a percent)		2.94%
Number of units owned by other limited partners		2,759,758
Number of shares reserved for conversion of units owned by other limited partners		2,826,426
Preferred stock, shares outstanding						9,200,000		7,700,000		4,000,000	22,658			60
Number of preferred units issued (in shares)												80,000	1,902,000
Preferred stock, dividend rate (as a percent)						6.50%		7.625%		7.875%	5.00%	6.00%	4.50%
Net proceeds from the offerings contributed by SL Green		221,965,000		122,041,000	222,200,000
Preferred stock, liquidation preference (in dollars per share)						$ 25.00		$ 25.00		$ 25.00	$ 1.00	$ 25.00	$ 25.00	$ 1,000.00
Preferred stock, annual distributions per share (in dollars per share)						$ 1.625		$ 1.90625		$ 1.96875		$ 1.50	$ 1.125
Conversion ratio, denominator (in dollars per unit)													$ 88.50
Common stock, shares authorized																				3,500,000
Number of shares redeemed							4,000,000		4,000,000
Redemption price (in dollars per share)							$ 25.00		$ 25.00
Cumulative and unpaid dividend (in dollars per share)							$ 0.3707		$ 0.4922
Preferred unit redemption costs	$ 10,010,000	$ 10,010,000					$ 6,300,000		$ 3,700,000