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

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.

No definition available.

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

Represents the number of units encompassing in residential properties.

No definition available.

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

Represents the weighted average occupancy of real estate properties owned, which represents the total leased square feet divided by the total available rentable square feet.

No definition available.

Name:	slg_RealEstateWeightedAverageOccupancy
Namespace Prefix:	slg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Area of a real estate property.

No definition available.

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

The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 60

-Paragraph 47

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(c))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph c

-Article 7

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

The number of real estate properties owned as of the balance sheet date.

No definition available.