Segment Information (Schedule of Reconciliation of Income from Continuing Operations to Net Income Attributable to SL Green Common Stockholders)(Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Reconciliation of income from continuing operations to net income attributable to SL Green common stockholders
Income (Loss) from continuing operations before equity in net gain on sale of interest in unconsolidated joint venture/real estate, gain on sale of real estate, depreciable real estate reserves net of recoveries, and loss on sale of investment in marketable securities	$ 42,721	$ 20,994	$ (18,927)	$ 33,272
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	225	15,281	43,588	16,050
Gain on sale of real estate, net	397	159,704	210,750	159,704
Depreciable real estate reserves	0	(19,226)	(10,387)	(19,226)
Loss on sale of investment in marketable securities	0	0	(83)	0
Income from continuing operations	43,343	176,753	224,941	189,800
Net income from discontinued operations	0	0	0	427
Gain on sale of discontinued operations	0	0	0	12,983
Net income	$ 43,343	$ 176,753	$ 224,941	$ 203,210