Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator
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
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)
Income attributable to SL Green common stockholders	$ 14,661	34,876	$ 195,177	250,358
Denominator
Common stock shares excluded from the diluted shares outstanding (shares)	2,131,606		1,779,212
SL Green Operating Partnership
Numerator
Net income attributable to SLGOP common unitholders	$ 14,661	34,876	$ 195,177	250,358
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)	14,328	34,768	194,259	249,992
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
Income attributable to SL Green common stockholders	$ 14,661	$ 34,876	$ 195,177	$ 250,358
Denominator
Basic weighted average common units outstanding (in shares)	77,049,000	86,550,000	79,644,000	87,138,000
Stock-based compensation plans (shares)	442,000	164,000	441,000	171,000
Diluted weighted average common units 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	1,317,803	1,779,212	1,266,296

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Incremental Common Units Attributable to Share based Payment Arrangements

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This element represents amounts attributable to ROP common unitholders.

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

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Weighted Average Number of Units Outstanding Diluted

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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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The total amount of dividends declared in the period for each class of stock and the contractual amount of dividends (or interest on participating income bonds) that must be paid for the period (for example, unpaid cumulative dividends). Dividends declared in the current period do not include dividends declared in respect of prior-period unpaid cumulative dividends. Preferred dividends that are cumulative only if earned are deducted only to the extent that they are earned.

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities, and addition from assumption of issuance of common shares for dilutive potential common shares; of income (loss) available to common shareholders.

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Weighted average number of limited partnership units outstanding determined by relating the portion of time within a reporting period that limited partnership units have been outstanding to the total time in that period.

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