Stockholders' Equity of the Company - Earnings per Share (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Basic Earnings:
(Loss) income attributable to SL Green common stockholders	$ (23,967)	$ 7,377	$ (423,892)	$ (28,748)
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)
Effect of Dilutive Securities:
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares	0	505	0	(484)
Add back: effect of dilutive securities (redemption of units to common shares)	(1,574)	491	(27,493)	(1,831)
Diluted Earnings:
Net (loss) income attributable to SL Green common stockholders, diluted	$ (25,949)	$ 7,868	$ (452,610)	$ (32,579)
Basic Shares:
Weighted average common shares outstanding (shares)	64,114,000	63,949,000	64,099,000	63,971,000
Effect of Dilutive Securities:
Operating Partnership units redeemable for common shares (shares)	4,182,000	4,088,000	4,175,000	4,104,000
Stock-based compensation plans (shares)	0	860,000	0	1,052,000
Contingently issuable shares (in shares)	0	0	0	122,000
Diluted weighted average common stock 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