Noncontrolling Interests in Operating Partnership (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		1 Months Ended		1 Months Ended				9 Months Ended	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Jan. 31, 2012 Series G Preferred Units	Sep. 30, 2012 Series G Preferred Units	Nov. 30, 2011 Series H Preferred Units	Sep. 30, 2012 Series H Preferred Units	Dec. 31, 2011 Series H Preferred Units	Sep. 30, 2012 Performance-based LTIP units	Sep. 30, 2012 SL Green Operating Partnership unit	Dec. 31, 2011 SL Green Operating Partnership unit
Organization
Noncontrolling interest in the operating partnership (as a percent)											3.53%	3.12%
Number of units of operating partnership owned by the noncontrolling interest unit holders											3,310,449	2,764,737
Phantom stock units outstanding (in shares)										66,668
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership											3,377,117
Number of preferred units issued (in shares)					1,902,000	1,902,000	80,000	80,000	80,000
Dividend rate preferred units (as a percent)					4.50%		6.00%
Liquidation preference of preferred units (in dollars per share)					$ 25.00	$ 25.00	$ 25.00	$ 25.00	$ 25.00
Annual dividends on preferred units (in dollars per share)					$ 1.125		$ 1.50
Operating partnership common stock value use for conversion of preferred units (in dollars per share)					$ 88.5
Number of company common stock issue on redemption of operation partnership common units					1
Rollforward analysis of the activity relating to the noncontrolling interests in the operating partnership
Balance at the beginning of period			$ 195,030								$ 195,030	$ 84,338
Distributions			(15,622)								(2,385)	(1,264)
Issuance of common units											40,542	60,443
Redemption of common units											(17,467)	(865)
Net income	567	170	4,876	13,946							4,876	14,629
Accumulated other comprehensive income allocation	(59)	(67)	(396)	(173)							(396)	(291)
Fair value adjustment											44,893	38,040
Balance at the end of period	$ 265,093		$ 265,093								$ 265,093	$ 195,030