Segment Information (Details 2) (USD $) In Thousands, 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
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 and purchase price fair value adjustments									$ 156,904	$ 124,144	$ 147,686
Equity in net gain 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										498,195
Income from continuing operations									193,957	625,257	276,607
Net income 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									209,700	677,122	319,156
Net income attributable to noncontrolling interests in operating partnership									(5,597)	(14,629)	(4,574)
Net income attributable to noncontrolling interests in other partnerships									(5,591)	(15,083)	(14,007)
Preferred units distribution									(2,107)
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