Name:	slg_DefinedContributionPlanEmployeeContributionLimitPercentageOfCompensation
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Data Type:	num:percentItemType
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Represents the employee contributions (as a percentage of compensation), which are matched by the employer by a specified percentage.

No definition available.

Name:	slg_DefinedContributionPlanEmployerMatchEmployeeContribution
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Data Type:	num:percentItemType
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Represents the employer matching contribution as a percent of the first specified percentage of employee contributions.

No definition available.

Name:	slg_DefinedContributionPlanEmployerMatchingContributionOfSpecifiedPercentageOfAnnualCompensation
Namespace Prefix:	slg_
Data Type:	num:percentItemType
Balance Type:	na
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Multiemployer Plans, Contributions By Employer, Percent

No definition available.

Name:	slg_MultiemployerPlansContributionsByEmployerPercent
Namespace Prefix:	slg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Name:	us-gaap_DefinedContributionPensionAndOtherPostretirementPlansDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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The amount of the cost recognized during the period for defined contribution plans.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 70

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942

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

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

Amount of contributions made to the multiemployer plan by all employers who participate in the plan. A multiemployer plan is a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 80

-Section 50

-Paragraph 7

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=14450570&loc=SL14450678-114947

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Data Type:	xbrli:monetaryItemType
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Name:	us-gaap_MultiemployerPlanTypeAxis=slg_HealthPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MultiemployerPlanTypeAxis=slg_MultiemployerPlansHealthPlanMember
Namespace Prefix:
Data Type:	na
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Period Type:

Name:	us-gaap_MultiemployerPlanTypeAxis=slg_MultiemployerPlansOtherPlansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_MultiemployerPlanTypeAxis=us-gaap_MultiemployerPlansPensionMember
Namespace Prefix:
Data Type:	na
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