Noncontrolling Interests in Operating Partnership (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		1 Months Ended			1 Months Ended				3 Months Ended	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Jan. 31, 2012 Series G Preferred Units	Mar. 31, 2013 Series G Preferred Units	Dec. 31, 2012 Series G Preferred Units	Nov. 30, 2011 Series H Preferred Units	Mar. 31, 2013 Series H Preferred Units	Dec. 31, 2012 Series H Preferred Units	Mar. 31, 2013 Performance Based LTIP units	Mar. 31, 2013 SL Green Operating Partnership unit	Dec. 31, 2012 SL Green Operating Partnership unit
Organization
Noncontrolling interest in the operating partnership (as a percent)										2.75%	2.94%
Number of units of operating partnership owned by the noncontrolling interest unit holders										2,585,675	2,759,758
Phantom stock units outstanding (in shares)									16,667
Shares of common stock reserved for issuance upon redemption of units of limited partnership interest in operating partnership										2,602,342
Number of preferred units issued (in shares)			1,902,000	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	$ 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)			$ 88.50
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	$ 212,907									$ 212,907	$ 195,030
Distributions	(4,879)									(853)	(3,296)
Issuance of common units										777	42,239
Redemption of common units										(17,287)	(87,513)
Net income	555	888								555	5,597
Accumulated other comprehensive income (loss) allocation	59	(184)								59	(388)
Fair value adjustment										24,016	61,238
Balance at the end of period	$ 220,174									$ 220,174	$ 212,907