Quarterly Financial Data (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Quarterly Financial Data (unaudited)
Total revenues	$ 328,877	$ 306,624	$ 298,705	$ 329,222	$ 262,785	$ 319,149	$ 251,684	$ 250,768	$ 1,263,428	$ 1,084,386	$ 978,361
Income net of noncontrolling interests and before gains on sale	1,833	9,544	10,176	72,898	14,563	81,340	16,687	20,674
Equity in net gain (loss) on sale of interest in unconsolidated joint venture/ real estate	(114)	3,032			1,633	520	126,769		2,918	128,921	6,691
Purchase price fair value adjustment	8,306	999	475,102	13,788					498,195
Gain on early extinguishment of debt		(67)	971			(511)	(1,276)	(113)	904	(1,900)	86,006
Gain (loss) on equity investment in marketable securities	4,999		(6)	(127)	775			(285)	4,866	490	(396)
Depreciable real estate reserves	(5,789)				(2,750)				(5,789)	(2,750)
Net income from discontinued operations	1,116	1,116	1,675	1,873	533	2,211	2,403	1,917	5,780	7,064	7,318
Gain (loss) on sale of discontinued operations			46,085			35,485			46,085	35,485	(6,841)
Net income (loss) attributable to SL Green	10,351	14,624	534,003	88,432	14,754	119,045	144,583	22,193	647,410	300,575	57,544
Preferred stock dividends	(7,543)	(7,545)	(7,545)	(7,545)	(7,545)	(7,545)	(7,545)	(7,114)	(30,178)	(29,749)	(19,875)
Net income attributable to SL Green common stockholders	$ 2,808	$ 7,079	$ 526,458	$ 80,887	$ 7,209	$ 111,500	$ 137,038	$ 15,079	$ 617,232	$ 270,826	$ 37,669
Net income (loss) per common share-Basic (in dollars per share)	$ 0.03	$ 0.08	$ 6.30	$ 1.02	$ 0.09	$ 1.43	$ 1.76	$ 0.19	$ 7.37	$ 3.47	$ 0.54
Net income (loss) per common share-Diluted (in dollars per share)	$ 0.03	$ 0.08	$ 6.26	$ 1.01	$ 0.09	$ 1.42	$ 1.75	$ 0.19	$ 7.33	$ 3.45	$ 0.54