Stockholders' Equity of the Company - Earnings per Share (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Basic Earnings:
(Loss) income attributable to SL Green common stockholders		$ (579,509)	$ (93,024)	$ 434,804
Less: distributed earnings allocated to participating securities		(2,655)	(2,219)	(2,398)
Less: undistributed earnings allocated to participating securities		0	0	(192)
Net (loss) income attributable to SL Green common stockholders (numerator for basic earnings per share)		(582,164)	(95,243)	432,214
Effect of Dilutive Securities:
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares		0	0	2,039
Add back: undistributed earnings allocated to participating securities		0	0	192
Add back: effect of dilutive securities (redemption of units to common shares)		(37,465)	(5,794)	25,457
Net (loss) income attributable to SL Green common stockholders, diluted		$ (619,629)	$ (101,037)	$ 459,902
Basic Shares:
Weighted average common stock outstanding (in shares)		63,809,000	63,917,000	65,740,000
Effect of Dilutive Securities:
Operating Partnership units redeemable for common shares (in shares)		4,163,000	4,012,000	3,987,000
Stock-based compensation plans (in shares)		0	0	705,000
Contingently issuable shares from special dividend declared December 4, 2020 (in shares)		0	0	337,000
Diluted weighted average common stock outstanding (in shares)		67,972,000	67,929,000	70,769,000
Common stock shares excluded from the diluted shares outstanding (in shares)		1,273,417	1,682,236	948,017