<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.22.4</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>27</ContextCount>
  <ElementCount>33</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>18</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>4</UnitCount>
  <MyReports>
    <Report instance="d461244dncsr.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 doctype="N-CSR" original="d461244dncsr.htm">d461244dncsr.htm</File>
    <File>cik0001308335-20230301.xsd</File>
    <File>cik0001308335-20230301_def.xml</File>
    <File>cik0001308335-20230301_lab.xml</File>
    <File>cik0001308335-20230301_pre.xml</File>
    <File>d461244dex9913c.htm</File>
    <File>d461244dex9913d.htm</File>
    <File>d461244dex99906cert.htm</File>
    <File>d461244dex99cert.htm</File>
  </InputFiles>
  <SupplementalFiles>
    <File>g461244img488b260e3.jpg</File>
    <File>g461244imga719f0442.gif</File>
    <File>g461244imge4d3dc604.jpg</File>
    <File>g461244imgf9e9578e1.gif</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="89">http://xbrl.sec.gov/cef/2022</BaseTaxonomy>
    <BaseTaxonomy items="4">http://xbrl.sec.gov/dei/2022</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>false</HasCalculationLinkbase>
</FilingSummary>
