Stockholders' Equity of the Company - Earnings per Share (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Basic Earnings (Loss):
Income (loss) attributable to SL Green common stockholders	$ 24,874	$ (13,279)	$ (7,293)	$ (2,298)
Less: distributed earnings allocated to participating securities	(519)	(435)	(1,561)	(1,309)
Net income (loss) attributable to SLGOP common unitholders (numerator for basic earnings per unit)	24,355	(13,714)	(8,854)	(3,607)
Effect of Dilutive Securities:
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares	0	0	0	0
Add back: effect of dilutive securities (redemption of units to common shares)	0	0	0	0
Income (loss) attributable to SL Green common stockholders (numerator for diluted earnings per share)	$ 24,355	$ (13,714)	$ (8,854)	$ (3,607)
Basic Shares:
Weighted average common shares outstanding (shares)	70,443,000	64,388,000	70,434,000	64,355,000
Effect of Dilutive Securities:
Operating Partnership units redeemable for common shares (shares)	0	0	0	0
Stock-based compensation plans (shares)	705,000	0	0	0
Diluted weighted average common stock outstanding (shares)	71,148,000	64,388,000	70,434,000	64,355,000
Common stock shares excluded from the diluted shares outstanding (shares)	5,633,308	5,345,430	6,358,175	5,155,662