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Significant Accounting Policies - Deferred Lease Costs (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Accounting Policies [Abstract] |  |  |
Portion of compensation capitalized | $ 6.8 | $ 6.6 | $ 6.2
Estimated average lease term (in years) | 7 years |  |

X
- Definition Represents the amount of deferred lease costs capitalized during the period. + References No definition available. + Details
Name: | slg_DeferredLeaseCostsCapitalizedInPeriod
Namespace Prefix: | slg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the estimated average term of the operating leases. + References No definition available. + Details
Name: | slg_OperatingLeasesEstimatedAverageLeaseTerm
Namespace Prefix: | slg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_AccountingPoliciesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration