Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Numerator
Less: distributed earnings allocated to participating securities	$ (369)	$ (333)	$ (738)	$ (444)
Less: undistributed earnings allocated to participating securities	(246)	0	0	(391)
Net Income attributable to common unitholders (numerator for basic earnings per unit)	104,717	56,111	97,130	170,410
Add back: dilutive effect of earnings allocated to participating securities	(369)	(333)	(738)	(444)
Add back: undistributed earnings allocated to participating securities	(246)	0	0	(391)
Income attributable to SL Green common stockholders	$ 111,614	59,514	$ 103,674	$ 180,517
Denominator
Common stock shares excluded from the diluted shares outstanding (shares)	993,847		1,064,788	1,597,015
SL Green Operating Partnership
Numerator
Net income attributable to SLGOP common unitholders	$ 111,614	59,514	$ 103,674	$ 180,517
Less: distributed earnings allocated to participating securities	(369)	(333)	(738)	(444)
Less: undistributed earnings allocated to participating securities	(246)	0	0	(391)
Net Income attributable to common unitholders (numerator for basic earnings per unit)	110,999	59,181	102,936	179,682
Add back: dilutive effect of earnings allocated to participating securities	369	333	738	444
Add back: undistributed earnings allocated to participating securities	246	0	0	391
Income attributable to SL Green common stockholders	$ 111,614	$ 59,514	$ 103,674	$ 180,517
Denominator
Basic weighted average common units outstanding (in shares)	73,073,000	77,658,000	73,117,000	78,768,000
Stock-based compensation plans (shares)	654,000	408,000	625,000	440,000
Contingently issuable units from special distribution declared December 4, 2020 (in shares)	0	0	157,000	0
Diluted weighted average common units outstanding (shares)	73,727,000	78,066,000	73,899,000	79,208,000
Common stock shares excluded from the diluted shares outstanding (shares)	993,847	2,130,084