Segment Information (Details 2) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
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, purchase price fair value adjustment, gain on sale of real estate and purchase price fair value adjustment	$ 20,994	$ 27,556	$ 33,272	$ 130,821
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	15,281	16,496	16,050	122,580
Depreciable real estate reserves	(19,226)	0	(19,226)	0
Purchase price fair value adjustment	0	(4,000)	0	67,446
Gain on sale of real estate	159,704	0	159,704	0
Income from continuing operations	176,753	40,052	189,800	320,847
Net income from discontinued operations	0	4,035	427	15,449
Gain on sale of discontinued operations	0	29,507	12,983	144,242
Net income	$ 176,753	$ 73,594	$ 203,210	$ 480,538