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Represents the amount of deferred lease costs capitalized during the period.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the number of investments accounted for under the equity method of accounting against which an other than temporary decline in value was recognized during the period.

+ References

No definition available.

+ Details

Name:	slg_EquityMethodInvestmentOtherThanTemporaryImpairmentNumber
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Data Type:	xbrli:integerItemType
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- Definition

The number of joint ventures to whom the entity provides guarantees in the form of recourse for debt.

+ References

No definition available.

+ Details

Name:	slg_NumberOfJointVenturesGuaranteedWithDebtRecourse
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- Definition

Represents the estimated average term of the operating leases.

+ References

No definition available.

+ Details

Name:	slg_OperatingLeasesEstimatedAverageLeaseTerm
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Data Type:	xbrli:durationItemType
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- Definition

This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 35

-Paragraph 32

-URI http://asc.fasb.org/extlink&oid=7658923&loc=d3e32787-111569

+ Details

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Period Type:	duration

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 4

-Subparagraph (b)(1)

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

+ Details

Name:	us-gaap_GuaranteeObligationsMaximumExposure
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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Significant Accounting Policies (Details 4) (USD $)	12 Months Ended
Significant Accounting Policies (Details 4) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010 investment
Investment in Unconsolidated Joint Ventures
Impairment charges recorded			$ 5,800,000
Number of investments with other than temporary impairment (investment)				1
Deferred Lease Costs
Portion of compensation capitalized	12,400,000	11,000,000	9,600,000
Estimated average lease term	7 years
Joint venture
Investment in Unconsolidated Joint Ventures
Recourse debt	$ 218,400,000
Number of joint ventures with debt recourse (joint ventures)	2