Stockholders' Equity of the Company - Earnings per Share (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Basic Earnings:
Income (loss) attributable to SL Green common stockholders	$ 7,377	$ 388,205	$ (28,748)	$ 486,073
Less: distributed earnings allocated to participating securities	(505)	(357)	(1,516)	(1,071)
Less: undistributed earnings allocated to participating securities	0	(1,977)	0	(1,790)
Net income (loss) attributable to SLGOP common unitholders (numerator for basic earnings per unit)	6,872	385,871	(30,264)	483,212
Effect of Dilutive Securities:
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares	505	357	(484)	1,071
Add back: undistributed earnings allocated to participating securities	0	1,977	0	1,790
Add back: effect of dilutive securities (redemption of units to common shares)	491	22,683	(1,831)	28,489
Diluted Earnings:
Net income (loss) attributable to SL Green common stockholders (numerator for diluted earnings per share)	$ 7,868	$ 410,888	$ (32,579)	$ 514,562
Basic Shares:
Weighted average common shares outstanding (shares)	63,949,000	64,856,000	63,971,000	66,248,000
Effect of Dilutive Securities:
Operating Partnership units redeemable for common shares (shares)	4,088,000	3,834,000	4,104,000	4,024,000
Stock-based compensation plans (shares)	860,000	806,000	1,052,000	676,000
Contingently issuable shares (in shares)	0	0	122,000	101,000
Diluted weighted average common stock outstanding (shares)	68,897,000	69,496,000	69,249,000	71,049,000
Common stock shares excluded from the diluted shares outstanding (shares)	621,134	969,631	517,574	1,032,243