Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Numerator
Less: distributed earnings allocated to participating securities	$ (408)	$ (505)	$ (1,225)	$ (1,516)
Net (loss) income attributable to SLGOP common unitholders (numerator for basic earnings per unit)	(24,375)	6,872	(425,117)	(30,264)
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares	0	(505)	0	484
Net (loss) income attributable to SL Green common stockholders, diluted	$ (25,949)	$ 7,868	$ (452,610)	$ (32,579)
Denominator
Common stock shares excluded from the diluted shares outstanding (shares)	1,402,771	621,134	1,380,364	517,574
SL Green Operating Partnership
Numerator
Net (loss) income attributable to SLGOP common unitholders (numerator for diluted earnings per unit)	$ (25,541)	$ 7,868	$ (451,385)	$ (30,579)
Less: distributed earnings allocated to participating securities	(408)	(505)	(1,225)	(1,516)
Net (loss) income attributable to SLGOP common unitholders (numerator for basic earnings per unit)	(25,949)	7,363	(452,610)	(32,095)
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares	0	505	0	(484)
Net (loss) income attributable to SL Green common stockholders, diluted	$ (25,949)	$ 7,868	$ (452,610)	$ (32,579)
Denominator
Basic weighted average common units outstanding (in shares)	68,296,000	68,037,000	68,274,000	68,075,000
Stock-based compensation plans (shares)	0	860,000	0	1,052,000
Contingently issuable units (in shares)	0	0	0	122,000
Diluted weighted average common units outstanding (shares)	68,296,000	68,897,000	68,274,000	69,249,000
Common stock shares excluded from the diluted shares outstanding (shares)	1,402,771	621,134	1,380,364	517,574