Noncontrolling Interests on the Company's Consolidated Financial Statements (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended			12 Months Ended	1 Months Ended			1 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 SL Green Operating Partnership	Dec. 31, 2013 SL Green Operating Partnership	Jan. 31, 2012 SL Green Operating Partnership Series G Preferred Units	Nov. 30, 2011 SL Green Operating Partnership Series H Preferred Units	Nov. 30, 2011 SL Green Operating Partnership Series F Preferred Units	Aug. 31, 2014 SL Green Operating Partnership Series K Preferred Units	Aug. 31, 2014 SL Green Operating Partnership Series L Preferred Units
Organization
Noncontrolling interest in the operating partnership (as a percent)					3.75%	2.96%
Number of units of operating partnership owned by the noncontrolling interest unit holders (shares)					3,735,478	2,902,317
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership (shares)					3,735,478
Number of preferred units issued (in shares)							1,902,000	80,000	60	563,954	378,634
Dividend rate preferred units (as a percent)							4.50%	6.00%		3.50%	4.00%
Liquidation preference of preferred units (in dollars per share)							$ 25.00	$ 25.00	$ 1,000	$ 25.00	$ 25.00
Number of preferred units authorized (in shares)										700,000	500,000
Annual dividends on preferred units (in dollars per share)							$ 1.125	$ 1.50		$ 0.875	$ 1.0
Operating partnership common stock value use for conversion of preferred units (in dollars per share)							$ 88.50			$ 135
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 beginning of period			$ 265,476		$ 265,476	$ 212,907
Distributions			(5,745)		(5,482)	(4,146)
Issuance of common units			28,058		22,862	24,750
Redemption of common units					(26,392)	(17,287)
Net income	2,636	1,110	16,010	1,909	16,010	3,023
Accumulated other comprehensive income allocation	113	(25)	347	490	347	611
Fair value adjustment					108,453	45,618
Balance at end of period	$ 381,274		$ 381,274		$ 381,274	$ 265,476