Stockholders' Equity of the Company - Earnings per Share (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Basic Earnings:
Income attributable to SL Green common stockholders	$ 161,103	$ 103,556	$ 204,895	$ 205,322
Net Income (Loss) Available To Common Stockholders, After Distributed And Undistributed Earnings Allocation, Basic	160,811	103,382	204,523	204,985
Effect of Dilutive Securities:
Add back: distributed earnings allocated to participating securities	128	119	257	237
Add back: undistributed earnings allocated to participating securities	164	55	115	100
Diluted Earnings:
Income attributable to SL Green common stockholders	$ 169,413	$ 109,142	$ 215,482	$ 216,180
Basic Shares:
Weighted average common shares outstanding (shares)	82,971,000	87,176,000	83,141,000	88,772,000
Effect of Dilutive Securities:
Operating Partnership units redeemable for common shares (shares)	4,260,000	4,706,000	4,296,000	4,695,000
Stock-based compensation plans (shares)	167,000	201,000	169,000	200,000
Diluted weighted average common stock outstanding (shares)	87,398,000	92,083,000	87,606,000	93,667,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,246,040	1,158,317
Common Stock
Effect of Dilutive Securities:
Redemption of units to common shares	$ 8,310	$ 5,586	$ 10,587	$ 10,858