Quarterly Financial Data (unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Quarterly Financial Data (unaudited)
Total revenues	$ 350,733	$ 361,385	$ 349,004	$ 339,133	$ 328,877	$ 306,624	$ 298,705	$ 329,222	$ 1,400,255	$ 1,263,428	$ 1,084,386
Income net of noncontrolling interests and before gains on sale	3,235	28,010	95,328	19,074	1,833	9,544	10,176	72,898
Equity in net gain (loss) on sale of interest in unconsolidated joint venture/ real estate	19,277	(4,807)	15,323	7,260	(114)	3,032			37,053	2,918	128,921
Purchase price fair value adjustment					8,306	999	475,102	13,788		498,195
Loss on early extinguishment of debt	(6,978)					(67)	971		(6,978)	904	(1,900)
Gain (loss) on sale of investment in marketable securities	2,703	2,237			4,999		(6)	(127)	4,900	4,500	1,900
Depreciable real estate reserves					(5,789)					(5,789)	(2,750)
Net income (loss) from discontinued operations	9,126	217	(67)	(160)	1,116	1,116	1,675	1,873	9,116	5,780	7,064
Gain on sale of discontinued operations				6,627			46,085		6,627	46,085	35,485
Net income attributable to SL Green	27,363	25,657	110,584	32,801	10,351	14,624	534,003	88,432	196,405	647,410	300,575
Preferred stock redemption costs		(10,010)							(10,010)
Preferred stock dividends	(7,407)	(7,915)	(7,544)	(7,545)	(7,543)	(7,545)	(7,545)	(7,545)	(30,411)	(30,178)	(29,749)
Net income attributable to SL Green common stockholders	$ 19,956	$ 7,732	$ 103,040	$ 25,256	$ 2,808	$ 7,079	$ 526,458	$ 80,887	$ 155,984	$ 617,232	$ 270,826
Net income per common share-Basic	$ 0.23	$ 0.09	$ 1.15	$ 0.29	$ 0.03	$ 0.08	$ 6.30	$ 1.02	$ 1.75	$ 7.37	$ 3.47
Net income per common share-Diluted	$ 0.23	$ 0.09	$ 1.14	$ 0.29	$ 0.03	$ 0.08	$ 6.26	$ 1.01	$ 1.74	$ 7.33	$ 3.45