Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Numerator
Less: distributed earnings allocated to participating securities	$ (1,835)	$ (2,655)	$ (2,219)
Net income (loss) attributable to SL Green common stockholders (numerator for basic earnings per share)	5,161	(582,164)	(95,243)
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares	$ 0	$ 0	$ 0
Denominator
Diluted weighted average common stock outstanding (in shares)	65,688,000	67,972,000	67,929,000
Common stock shares excluded from the diluted shares outstanding (in shares)	4,717,759
SL Green Operating Partnership
Numerator
Net Income (loss) attributable to SLGOP common unitholders (numerator for diluted earnings per unit)	$ 7,557	$ (616,974)	$ (98,818)
Less: distributed earnings allocated to participating securities	(4,665)	(2,655)	(2,219)
Net income (loss) attributable to SL Green common stockholders (numerator for basic earnings per share)	2,892	(619,629)	(101,037)
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares	26	0	0
Income (loss) attributable to SLGOP common unitholders	$ 2,918	$ (619,629)	$ (101,037)
Denominator
Basic weighted average common units outstanding (in shares)		67,972,000	67,929,000
Stock-based compensation plans (in shares)	757,000	0	0
Contingently issuable units (in shares)	112,000	0	0
Diluted weighted average common stock outstanding (in shares)	69,605,000	67,972,000	67,929,000
Common stock shares excluded from the diluted shares outstanding (in shares)	800,881	1,273,417	1,682,236