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Mortgages and Other Loans Payable - Narrative (Details) - USD ($) $ in Billions | Dec. 31, 2023 | Dec. 31, 2022
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Mortgages and Other Loans Payable |  |
Book value of collateral | $ 1.9 | $ 3.8

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- Definition -- None. No documentation exists for this element. -- + References No definition available. + Details
Name: | slg_MortgagesAndOtherLoansPayableDisclosureAbstract
Namespace Prefix: | slg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4H -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480434/815-10-50-4H + Details
Name: | us-gaap_CollateralAlreadyPostedAggregateFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant