Segment Information (Schedule of Reconciliation of Income from Continuing Operations to Net Income Attributable to SL Green Common Stockholders)(Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reconciliation of income from continuing operations to net income attributable to SL Green common stockholders
(Loss) Income 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	$ (70,463,000)	$ (29,948,000)	$ (61,648,000)	$ 12,278,000
Equity in net gain on sale of interest in unconsolidated joint venture/real estate	33,448,000	769,000	43,363,000	769,000
Gain on sale of real estate, net	196,580,000	0	210,353,000.00	0
Depreciable real estate reserves	(10,387,000)	0	(10,387,000)	0
Loss on sale of investment in marketable securities	(83,000)	0	(83,000)	0
Income (loss) from continuing operations	149,095,000	(29,179,000)	181,598,000	13,047,000
Net income (loss) from discontinued operations	0	0	0	427,000
Gain on sale of discontinued operations	0	0	0	12,983,000
Net income (loss)	$ 149,095,000	$ (29,179,000)	$ 181,598,000	$ 26,457,000