Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Numerator
Net Income (Loss) Available To Common Stockholders, After Distributed And Undistributed Earnings Allocation, Basic	$ 160,811	$ 103,382	$ 204,523	$ 204,985
Add back: distributed earnings allocated to participating securities	128	119	257	237
Add back: undistributed earnings allocated to participating securities	164	55	115	100
Income attributable to SL Green common stockholders	$ 169,413	$ 109,142	$ 215,482	$ 216,180
Denominator
Weighted average common shares outstanding (shares)	82,971,000	87,176,000	83,141,000	88,772,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,246,040	1,158,317
SL Green Operating Partnership
Numerator
Net income attributable to SLGOP common unitholders	$ 169,413	$ 109,142	$ 215,482	$ 216,180
Less: distributed earnings allocated to participating securities	(128)	(119)	(257)	(237)
Less: undistributed earnings allocated to participating securities	(164)	(55)	(115)	(100)
Net Income (Loss) Available To Common Stockholders, After Distributed And Undistributed Earnings Allocation, Basic	169,121	108,968	215,110	215,843
Add back: distributed earnings allocated to participating securities	128	119	257	237
Add back: undistributed earnings allocated to participating securities	164	55	115	100
Income attributable to SL Green common stockholders	$ 169,413	$ 109,142	$ 215,482	$ 216,180
Denominator
Basic weighted average common units outstanding (in shares)	87,231,000	91,882,000	87,437,000	93,467,000
Stock-based compensation plans (shares)	167,000	201,000	169,000	200,000
Diluted weighted average common units 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	1,241,778	1,184,735