Segment Information (Schedule of Reconciliation of Income from Continuing Operations to Net Income Attributable to SL Green Common Stockholders)(Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 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, depreciable real estate reserves, loss on early extinguishment of debt, and loss (gain) on sale of marketable securities	$ 7,256	$ 90,289	$ 201,500
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	44,009	15,844	123,253
Purchase price fair value adjustment	0	40,078	67,446
Gain on sale of real estate, net	238,116	175,974	0
Depreciable real estate reserves	(10,387)	(19,226)	0
Loss on early extinguishment of debt	0	(49)	(32,365)
(Loss) gain on sale of investment in marketable securities	(83)	0	3,895
Income from continuing operations	278,911	302,910	363,729
Net income from discontinued operations	0	427	19,075
Gain on sale of discontinued operations	0	14,122	163,059
Net income	$ 278,911	$ 317,459	$ 545,863