Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator
Less: distributed earnings allocated to participating securities	$ (363)	$ (333)	$ (1,090)	$ (777)
Less: undistributed earnings allocated to participating securities	(1,942)	0	(1,736)	(141)
Net Income attributable to common unitholders (numerator for basic earnings per unit)	385,900	13,526	483,247	184,186
Add back: dilutive effect of earnings allocated to participating securities	(363)	(333)	(1,090)	(777)
Add back: undistributed earnings allocated to participating securities	(1,942)	0	(1,736)	(141)
Income attributable to SL Green common stockholders	$ 410,888	14,661	$ 514,562	$ 195,177
Denominator
Common stock shares excluded from the diluted shares outstanding (shares)	969,631		1,032,243	1,728,767
SL Green Operating Partnership
Numerator
Net income attributable to SLGOP common unitholders	$ 410,888	14,661	$ 514,562	$ 195,177
Less: distributed earnings allocated to participating securities	(363)	(333)	(1,090)	(777)
Less: undistributed earnings allocated to participating securities	(1,942)	0	(1,736)	(141)
Net Income attributable to common unitholders (numerator for basic earnings per unit)	408,583	14,328	511,736	194,259
Add back: dilutive effect of earnings allocated to participating securities	363	333	1,090	777
Add back: undistributed earnings allocated to participating securities	1,942	0	1,736	141
Income attributable to SL Green common stockholders	$ 410,888	$ 14,661	$ 514,562	$ 195,177
Denominator
Basic weighted average common units outstanding (in shares)	70,674,000	74,972,000	72,299,000	77,496,000
Stock-based compensation plans (shares)	813,000	442,000	684,000	441,000
Contingently issuable units from special distribution declared December 4, 2020 (in shares)	0	0	104,000	0
Diluted weighted average common units outstanding (shares)	71,487,000	75,414,000	73,087,000	77,937,000
Common stock shares excluded from the diluted shares outstanding (shares)	969,631	2,071,169

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Incremental Common Units Attributable to Dilutive Effect of Nonvested Shares with Forfeitable Dividends

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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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Amount of undistributed earnings (loss) allocated to participating securities for the basic earnings (loss) per share or per unit calculation under the two-class method.

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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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