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

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

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
Period Type:	duration

Represents the quarterly amount of contributions made to the multiemployer plan by all employers that were diverted from the Health Plan to the Pension Plan pursuant to the contribution diversion provision in the collective bargaining agreements. Diversions were effective beginning January 1, 2009 and ending October 1, 2010.

No definition available.

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

- Details

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

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

- Details

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