Segment Information (Details 2) (USD $) In Thousands, 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
Reconciliation of income from continuing operations to net income attributable to SL Green common stockholders
Income from continuing operations before equity in net gain on sale of unconsolidated joint venture/ partial interest and purchase price fair value adjustments									$ 124,144	$ 147,686	$ 64,497
Equity in net gain 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
Income from continuing operations									625,257	276,607	71,188
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									677,122	319,156	71,665
Net income attributable to noncontrolling interests in the operating partnership									(14,629)	(4,574)	(1,221)
Net income attributable to noncontrolling interests in other partnerships									(15,083)	(14,007)	(12,900)
Net income 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