<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.25.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>30</ContextCount>
  <ElementCount>18</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>6</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>4</UnitCount>
  <MyReports>
    <Report instance="glu_ncsrs.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>995470 - Disclosure - N-2</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/cef/role/N2</Role>
      <ShortName>N-2</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>glu-20250630.xsd</File>
    <File>glu-20250630_def.xml</File>
    <File>glu-20250630_lab.xml</File>
    <File>glu-20250630_pre.xml</File>
    <File doctype="N-CSRS" isDefinitelyNotFs="true" isNcsr="true" isUsgaap="true" original="glu_ncsrs.htm">glu_ncsrs.htm</File>
  </InputFiles>
  <SupplementalFiles>
    <File>glu_001.jpg</File>
    <File>glu_002.jpg</File>
    <File>glu_003.jpg</File>
    <File>glu_back.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="13">http://fasb.org/us-gaap/2025</BaseTaxonomy>
    <BaseTaxonomy items="62">http://xbrl.sec.gov/cef/2025</BaseTaxonomy>
    <BaseTaxonomy items="5">http://xbrl.sec.gov/dei/2025</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>false</HasCalculationLinkbase>
</FilingSummary>
