Represents the value of land as a percentage of the fair market value of the property under lease.

No definition available.

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- Definition

Represents the annual ground lease payments required to be made under the operating sub-leasehold position.

+ References

No definition available.

+ Details

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

- Definition

Operating Leases, Annual Ground Lease Payments, Due After Year Sixteen

+ References

No definition available.

+ Details

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

- Definition

Operating Leases, Annual Ground Lease Payments, Next Six Years

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Operating Leases, Annual Ground Lease Payments, Year Seven to Year Sixteen

+ References

No definition available.

+ Details

Name:	slg_OperatingLeasesAnnualGroundLeasePaymentsYearSeventoYearSixteen
Namespace Prefix:	slg_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the number of renewal options available for the operating lease.

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of the fee interest in the sub-leasehold position not owned by the entity.

+ References

No definition available.

+ Details

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

- Definition

Represents the term of the first renewal option available for the operating lease.

+ References

No definition available.

+ Details

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Namespace Prefix:	slg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the term of the second renewal option available for the operating lease.

+ References

No definition available.

+ Details

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Namespace Prefix:	slg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the term of the third renewal option available for the operating lease.

+ References

No definition available.

+ Details

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Namespace Prefix:	slg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount before accumulated depreciation of leased physical assets used in the normal conduct of business to produce goods and services.

+ References

+ Details

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

- Definition

The total charge for the use of long-lived depreciable assets subject to a lease meeting the criteria for capitalization.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 30

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6455314&loc=d3e45014-112735

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 10

-Section 55

-Paragraph 40

-Subparagraph (Note 2)

-URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697

+ Details

Name:	us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassAccumulatedDeprecation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Cash payments to lessor's for use of assets under operating leases.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585

+ Details

Name:	us-gaap_PaymentsForRent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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

- Details

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- Details

Name:	slg_LeasePaymentPeriodAxis=slg_ThroughJuly2016Member
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	slg_RealEstateByLocationAxis=slg_AmsterdamAvenue1080Member
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	slg_RealEstateByLocationAxis=slg_AvenueOfTheAmericas1185Member
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Balance Type:
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- Details

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- Details

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- Details

Name:	slg_RealEstateByLocationAxis=slg_MadisonAvenue625Member
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- Details

Name:	slg_RealEstateByLocationAxis=slg_ThirdAvenue711Member
Namespace Prefix:
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Commitments and Contingencies (Details 2) (USD $)	12 Months Ended	1 Months Ended
Commitments and Contingencies (Details 2) (USD $)	Dec. 31, 2014 extenstion_option	Oct. 31, 2012	Jul. 31, 2011	Dec. 31, 2013
Commitments and Contingencies
Cost basis	$ 27,445,000us-gaap_CapitalLeasedAssetsGross			$ 50,310,000us-gaap_CapitalLeasedAssetsGross
420 Lexington Avenue
Commitments and Contingencies
Number of renewal options available (extension option)	2
Annual ground lease payments through December 2019	10,900,000
Annual ground lease payments through December 2029	11,200,000
Annual ground lease payments due thereafter	12,300,000
Value of land as a percentage of the fair market value of the property (percent)	6.00%
1080 Amsterdam Avenue
Commitments and Contingencies
Value of land as a percentage of the fair market value of the property (percent)		40.00%
Prepayment of ground lease rent		13,000,000
Cost basis	27,400,000
Cumulative amortization	400,000
711 Third Avenue
Commitments and Contingencies
Percentage of fee not owned by the entity (percent)			50.00%
461 Fifth Avenue
Commitments and Contingencies
Number of renewal options available (extension option)	2
Required annual ground lease payments	2,100,000
Term of first renewal option	21 years
Term of second renewal option	21 years
Term of third renewal option	15 years
625 Madison Avenue
Commitments and Contingencies
Number of renewal options available (extension option)	2
Required annual ground lease payments	4,600,000
Term of first renewal option	23 years
Term of second renewal option	23 years
1185 Avenue of the Americas
Commitments and Contingencies
Required annual ground lease payments	6,900,000
Term of first renewal option	23 years
Through July 2016 \| 711 Third Avenue
Commitments and Contingencies
Required annual ground lease payments	5,250,000
After July 2016 \| 711 Third Avenue
Commitments and Contingencies
Required annual ground lease payments	$ 5,500,000