<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.26.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>93</ContextCount>
  <ElementCount>37</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>12</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>2</UnitCount>
  <MyReports>
    <Report instance="tm261543-1_def14a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>995100 - Document - Cover</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/dei/role/document/Cover</Role>
      <ShortName>Cover</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="tm261543-1_def14a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>995410 - Disclosure - Pay vs Performance Disclosure</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/PvpDisclosure</Role>
      <ShortName>Pay vs Performance Disclosure</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="tm261543-1_def14a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>995440 - Disclosure - Recovery of Erroneously Awarded Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/ErrCompDisclosure</Role>
      <ShortName>Recovery of Erroneously Awarded Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="tm261543-1_def14a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>995443 - Disclosure - Award Timing Disclosure</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/AwardTimingDisclosure</Role>
      <ShortName>Award Timing Disclosure</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="tm261543-1_def14a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>995447 - Disclosure - Insider Trading Policies and Procedures</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingPoliciesProc</Role>
      <ShortName>Insider Trading Policies and Procedures</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>slg-20251231.xsd</File>
    <File>slg-20251231_def.xml</File>
    <File>slg-20251231_lab.xml</File>
    <File doctype="DEF 14A" isProxy="true" isUsgaap="true" original="tm261543-1_def14a.htm">tm261543-1_def14a.htm</File>
  </InputFiles>
  <SupplementalFiles>
    <File>bc_netincome-pn.jpg</File>
    <File>bc_normalized-pn.jpg</File>
    <File>bc_peergroup-pn.jpg</File>
    <File>bc_tsr-pn.jpg</File>
    <File>cv_ofc-4clr.jpg</File>
    <File>fc_esgoversight-pn.jpg</File>
    <File>ic_academia-pn.jpg</File>
    <File>ic_accounting-pn.jpg</File>
    <File>ic_arrow-pn.jpg</File>
    <File>ic_business-pn.jpg</File>
    <File>ic_byinternet-pn.jpg</File>
    <File>ic_bylaws-pn.jpg</File>
    <File>ic_bytelephone-pn.jpg</File>
    <File>ic_circlehalf-pn.jpg</File>
    <File>ic_corporate-pn.jpg</File>
    <File>ic_diversity-pn.jpg</File>
    <File>ic_do-bw.jpg</File>
    <File>ic_dont-bw.jpg</File>
    <File>ic_environmental-pn.jpg</File>
    <File>ic_esgoversight-pn.jpg</File>
    <File>ic_executive-pn.jpg</File>
    <File>ic_experience-pn.jpg</File>
    <File>ic_finance-pn.jpg</File>
    <File>ic_four-pn.jpg</File>
    <File>ic_government-pn.jpg</File>
    <File>ic_human-pn.jpg</File>
    <File>ic_leadership-pn.jpg</File>
    <File>ic_location-pn.jpg</File>
    <File>ic_one-pn.jpg</File>
    <File>ic_proxy-pn.jpg</File>
    <File>ic_qrcode-pn.jpg</File>
    <File>ic_record-pn.jpg</File>
    <File>ic_response-pn.jpg</File>
    <File>ic_risk-pn.jpg</File>
    <File>ic_talent-pn.jpg</File>
    <File>ic_technology-pn.jpg</File>
    <File>ic_three-pn.jpg</File>
    <File>ic_tick-pn.jpg</File>
    <File>ic_tickcircle-pn.gif</File>
    <File>ic_tickcircle-pn.jpg</File>
    <File>ic_time-pn.jpg</File>
    <File>ic_triangle-pn.jpg</File>
    <File>ic_two-pn.jpg</File>
    <File>lg_slgreen-4c.jpg</File>
    <File>pc_eightyeightpcnt-pn.jpg</File>
    <File>pc_fiftypercent-pn.jpg</File>
    <File>pc_majority-pn.jpg</File>
    <File>pc_thirtyeightpcnt-pn.jpg</File>
    <File>ph_andrewmathias-bwlr.jpg</File>
    <File>ph_businessoverview-4clr.jpg</File>
    <File>ph_carobrown-4clr.jpg</File>
    <File>ph_craighatkoff-bwlr.jpg</File>
    <File>ph_harrisonsitomer-bw.jpg</File>
    <File>ph_johnalschuler-4clr.jpg</File>
    <File>ph_laurendillard-bwlr.jpg</File>
    <File>ph_levine-bwlr.jpg</File>
    <File>ph_marcholliday-bwlr.jpg</File>
    <File>ph_mattdiliberto-bwlr.jpg</File>
    <File>ph_peggylamb-bw.jpg</File>
    <File>ph_stephengreen-bwlr.jpg</File>
    <File>px_26slgreenproxy01pg01-bw.jpg</File>
    <File>px_26slgreenproxy01pg02-bw.jpg</File>
    <File>sg_andrewlevine-bw.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="5">http://fasb.org/us-gaap/2025</BaseTaxonomy>
    <BaseTaxonomy items="4">http://xbrl.sec.gov/dei/2025</BaseTaxonomy>
    <BaseTaxonomy items="175">http://xbrl.sec.gov/ecd/2025</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>false</HasPresentationLinkbase>
  <HasCalculationLinkbase>false</HasCalculationLinkbase>
</FilingSummary>
