Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Basic Earnings (Loss):
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)
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable 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)
SL Green Operating Partnership
Basic Earnings (Loss):
Net income (loss) attributable to SLGOP common unitholders	26,611	(14,193)	(7,796)	(2,464)
Less: distributed earnings allocated to participating securities	(1,239)	(1,147)	(3,725)	(3,415)
Net income (loss) attributable to SLGOP common unitholders (numerator for basic earnings per unit)	25,372	(15,340)	(11,521)	(5,879)
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares	213	0	0	0
Income (loss) attributable to SL Green common stockholders (numerator for diluted earnings per share)	$ 25,585	$ (15,340)	$ (11,521)	$ (5,879)
Denominator
Basic weighted average common units outstanding (in shares)	74,318	67,999	74,433	68,092
Stock-based compensation plans (in shares)	798	0	0	0
Contingently issuable units (in shares)	519	0	0	0
Diluted weighted average common units outstanding (in shares)	75,635	67,999	74,433	68,092