Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Numerator
Net income attributable to SL Green common stockholders (numerator for basic earnings per share)	$ 432,214	$ 354,283	$ 253,784
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares	2,039	1,685	1,700
Add back: undistributed earnings allocated to participating securities	$ (192)	$ (137)	$ 0
Denominator
Weighted average common stock outstanding (in shares)	65,740,000	70,397,000	77,057,000
Diluted weighted average common stock outstanding (in shares)	70,769,000	75,078,000	81,865,000
Common stock shares excluded from the diluted shares outstanding (shares)	948,017	1,676,825	1,181,014
SL Green Operating Partnership
Numerator
Net income attributable to SLGOP common unitholders	$ 460,261	$ 376,121	$ 268,785
Less: distributed earnings allocated to participating securities	(2,398)	(1,685)	(1,700)
Undistributed Earnings (Loss) Allocated to Participating Securities, Basic	(192)	(137)	0
Net income attributable to SL Green common stockholders (numerator for basic earnings per share)	457,671	374,299	267,085
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares	2,590	1,822	1,700
Income attributable to SLGOP common unitholders	$ 460,261	$ 376,121	$ 268,785
Denominator
Weighted average common stock outstanding (in shares)	69,667,000	74,493,000	81,332,000
Stock-based compensation plans (shares)	765,000	441,000	543,000
Contingently issuable units from special dividend declared December 4, 2020 (in shares)	337,000	144,000	(10,000)
Diluted weighted average common stock outstanding (in shares)	70,769,000	75,078,000	81,865,000