Segment Information (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
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 interest in unconsolidated joint venture/real estate and purchase price fair value adjustment									$ 173,030	$ 109,400	$ 133,780
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	673	16,496	1,444	104,640	7,538	(354)	(3,583)	0	123,253	3,601	37,053
Purchase price fair value adjustment									67,446	(2,305)	0
Income from continuing operations									363,729	110,696	170,833
Net income from discontinued operations	3,626	4,035	5,645	5,769	5,836	7,435	5,943	6,473	19,075	25,687	32,240
Gain on sale of discontinued operations	18,817	29,507	114,735	0	0	13,787	0	1,113	163,059	14,900	6,627
Net income									$ 545,863	$ 151,283	$ 209,700