Significant Accounting Policies - Concentrations of Credit Risk (Narrative) (Details)	12 Months Ended
Dec. 31, 2024 agreement tenant
Annualized Rent \| Customer Concentration
Concentration of Credit Risk
Number of tenants (tenants) \| tenant	1
Maximum percentage of annualized rent for any one tenant not individually disclosed (percent) (more than)	5.00%
Annualized Rent \| Customer Concentration \| Tenant 1
Concentration of Credit Risk
Percentage of concentration (percent)	5.50%
Collective Bargaining Arrangements \| Workforce Concentration
Concentration of Credit Risk
Percentage of concentration (percent)	57.20%
Number of collective bargaining agreements \| agreement	5
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year \| Workforce Concentration
Concentration of Credit Risk
Percentage of concentration (percent)	0.00%

Represents the maximum percentage of concentration risk that is not individually disclosed.

No definition available.

Name:	slg_ConcentrationRiskPercentageThreshold
Namespace Prefix:	slg_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the number of collective bargaining arrangements.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of tenants to whom the facility is leased.

+ References

No definition available.

+ Details

Name:	slg_NumberOfTenants
Namespace Prefix:	slg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 954
-SubTopic 310
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478785/954-310-50-2

+ Details

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

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 42
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-42

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-21

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-20

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482861/275-10-50-18

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482861/275-10-50-20

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=slg_AnnualizedRentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MajorCustomersAxis=slg_Tenant1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_WorkforceSubjectToCollectiveBargainingArrangementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_LaborForceConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_WorkforceSubjectToCollectiveBargainingArrangementsExpiringWithinOneYearMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: