Debt Investments, Other

No definition available.

Name:	slg_DebtInvestmentsOther
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Mortgage Loans on Real Estate, Commercial and Consumer, Net Including Debt Investments, Other

+ References

No definition available.

+ Details

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Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the number of shares of the common stock of the entity, which the limited partner of the operating partnership is entitled to receive on redemption of one unit of interest in the partnership.

+ References

No definition available.

+ Details

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

- Definition

Number of Real Estate Buildings

+ References

No definition available.

+ Details

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Namespace Prefix:	slg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

-- None. No documentation exists for this element. --

+ References

No definition available.

+ Details

Name:	slg_OwnershipInterestsLineItems
Namespace Prefix:	slg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Area of a real estate property.

+ References

No definition available.

+ Details

Name:	us-gaap_AreaOfRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of asset acquired in business combination and recognized at acquisition date.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 805
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479907/805-20-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 805
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479907/805-20-50-1

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of units or percentage investment held in the subsidiary by the limited liability company or limited partnership.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=slg_MadisonAvenue346And11East44thStreetMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=srt_OfficeBuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=srt_RetailSiteMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=slg_ManagedOfficePropertiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=slg_ServiceCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_SubsidiariesMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	dei_LegalEntityAxis=slg_SLGreenManagementMember
Namespace Prefix:
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- Details

Name:	srt_OwnershipAxis=slg_SLGManagementLLCMember
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Organization and Basis of Presentation - Additional Information (Details) ft² in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2025 USD ($) ft² building shares	Oct. 31, 2025 USD ($)	Dec. 31, 2024
Organization
Number of shares to be received on redemption of one unit of limited partnership interests (shares) \| shares	1
Madison Avenue, 346 and 11 East 44th Street \| Subsequent Event
Organization
Gross asset valuation		$ 160.0
Office Building
Organization
Number of buildings \| building	1
Retail Site
Organization
Number of buildings \| building	1
Managed Office Properties
Organization
Approximate square feet \| ft²	0.4
Debt and preferred equity investments including investments held by unconsolidated joint ventures	$ 171.4
Debt and preferred equity investments and other financing receivables included in other balance sheet items	$ 130.5
Service Corporation
Organization
Percentage of ownership in SL Green Management LLC owned by operating partnership (percent)	95.00%
Operating Partnership \| SL Green Operating Partnership
Organization
Noncontrolling interest in the operating partnership (as a percent)	6.39%		5.97%
SL Green Management \| SL Green Management LLC
Organization
Percentage of ownership in SL Green Management LLC owned by operating partnership (percent)	100.00%