Stockholders' Equity of the Company - Earnings per Share (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Basic Earnings:
Income attributable to SL Green common stockholders	$ 13,859	$ 33,157	$ 185,104	$ 238,052
Less: distributed earnings allocated to participating securities	(333)	(108)	(777)	(325)
Less: undistributed earnings allocated to participating securities	0	0	(141)	(41)
Net Income attributable to common unitholders (numerator for basic earnings per unit)	13,526	33,049	184,186	237,686
Effect of Dilutive Securities:
Add back: dilutive effect of earnings allocated to participating securities	333	108	777	325
Add back: undistributed earnings allocated to participating securities	0	0	141	41
Redemption of units to common shares	802	1,719	10,073	12,306
Diluted Earnings:
Income attributable to SL Green common stockholders	$ 14,661	$ 34,876	$ 195,177	$ 250,358
Basic Shares:
Weighted average common shares outstanding (shares)	73,020,000	82,292,000	75,521,000	82,855,000
Effect of Dilutive Securities:
Operating Partnership units redeemable for common shares (shares)	4,029,000	4,258,000	4,123,000	4,283,000
Stock-based compensation plans (shares)	442,000	164,000	441,000	171,000
Diluted weighted average common stock outstanding (shares)	77,491,000	86,714,000	80,085,000	87,309,000
Common stock shares excluded from the diluted shares outstanding (shares)	2,131,606		1,779,212

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Net Income (Loss) Available To Common Stockholders, After Distributed And Undistributed Earnings Allocation, Basic

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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