Partners' Capital of the Operating Partnership - EPS (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Numerator
Less: distributed earnings allocated to participating securities	$ (497)	$ (362)	$ (995)	$ (725)
Less: undistributed earnings allocated to participating securities	0	(261)	0	0
Net (loss) income attributable to SLGOP common unitholders (numerator for basic earnings per unit)	(44,373)	104,709	(37,120)	97,143
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares	1,103	(362)	806	(725)
Add back: undistributed earnings allocated to participating securities	0	(261)	0	0
Net (loss) income attributable to SL Green common stockholders (numerator for diluted earnings per share)	$ (48,289)	$ 111,614	$ (40,247)	$ 103,674
Denominator
Common stock shares excluded from the diluted shares outstanding (shares)	528,607	964,338	482,130	1,033,173
SL Green Operating Partnership
Numerator
Net (loss) income attributable to SLGOP common unitholders (numerator for diluted earnings per unit)	$ (46,689)	$ 111,614	$ (38,446)	$ 103,674
Less: distributed earnings allocated to participating securities	(497)	(362)	(995)	(725)
Less: undistributed earnings allocated to participating securities	0	(261)	0	0
Net (loss) income attributable to SLGOP common unitholders (numerator for basic earnings per unit)	(47,186)	110,991	(39,441)	102,949
Add back: dilutive effect of earnings allocated to participating securities and contingently issuable shares	(1,103)	362	(806)	725
Add back: undistributed earnings allocated to participating securities	0	261	0	0
Net (loss) income attributable to SL Green common stockholders (numerator for diluted earnings per share)	$ (48,289)	$ 111,614	$ (40,247)	$ 103,674
Denominator
Basic weighted average common units outstanding (in shares)	67,900,000	71,024,000	68,099,000	71,069,000
Stock-based compensation plans (shares)	1,120,000	648,000	1,139,000	616,000
Contingently issuable units (in shares)	0	0	184,000	153,000
Diluted weighted average common units outstanding (shares)	69,020,000	71,672,000	69,422,000	71,838,000
Common stock shares excluded from the diluted shares outstanding (shares)	528,607	964,338	482,130	1,033,173

Distributed Earnings, Diluted

No definition available.

Name:	slg_DistributedEarningsDiluted
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	slg_IncrementalCommonUnitsAttributableToDilutiveEffectOfNonvestedSharesWithForfeitableDividends
Namespace Prefix:	slg_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Incremental Common Units Attributable to Share based Payment Arrangements

+ References

No definition available.

+ Details

Name:	slg_IncrementalCommonUnitsAttributabletoSharebasedPaymentArrangements
Namespace Prefix:	slg_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents amounts attributable to ROP common unitholders.

+ References

No definition available.

+ Details

Name:	slg_NetIncomeLossAllocatedToCommonUnitholders
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	slg_NetIncomeLossAvailableToCommonStockholdersAfterDistributedAndUndistributedEarningsAllocationBasic
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Weighted Average Number of Units Outstanding Diluted

+ References

No definition available.

+ Details

Name:	slg_WeightedAverageNumberofUnitsOutstandingDiluted
Namespace Prefix:	slg_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=124432515&loc=d3e3550-109257

+ Details

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60B
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126958026&loc=SL5780133-109256

+ Details

Name:	us-gaap_DistributedEarnings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_NetIncomeLossAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 40
-Subparagraph (b)(2)
-URI https://asc.fasb.org/extlink&oid=126958026&loc=d3e1930-109256

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 40
-Subparagraph (b)(3)
-URI https://asc.fasb.org/extlink&oid=126958026&loc=d3e1930-109256

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60B
-Subparagraph (c)
-URI https://asc.fasb.org/extlink&oid=126958026&loc=SL5780133-109256

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=124432515&loc=d3e3550-109257

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 40
-Subparagraph (b)(1)
-URI https://asc.fasb.org/extlink&oid=126958026&loc=d3e1930-109256

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 16
-URI https://asc.fasb.org/extlink&oid=126958026&loc=d3e1505-109256

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 40
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126958026&loc=d3e1930-109256

+ Details

Name:	us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 65
-URI https://asc.fasb.org/extlink&oid=126958026&loc=d3e2793-109256

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60B
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126958026&loc=SL5780133-109256

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 66
-URI https://asc.fasb.org/extlink&oid=126958026&loc=d3e2814-109256

+ Details

Name:	us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesBasic
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60
-URI https://asc.fasb.org/extlink&oid=126958026&loc=d3e2740-109256

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 65
-URI https://asc.fasb.org/extlink&oid=126958026&loc=d3e2793-109256

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60B
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126958026&loc=SL5780133-109256

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 66
-URI https://asc.fasb.org/extlink&oid=126958026&loc=d3e2814-109256

+ Details

Name:	us-gaap_UndistributedEarningsLossAllocatedToParticipatingSecuritiesDiluted
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB Topic 4.F)
-URI https://asc.fasb.org/extlink&oid=120397183&loc=d3e187171-122770

+ Details

Name:	us-gaap_WeightedAverageLimitedPartnershipUnitsOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: