<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.26.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>169</ContextCount>
  <ElementCount>253</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>43</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>11</UnitCount>
  <MyReports>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0000001 - Document - Cover Page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/CoverPage</Role>
      <ShortName>Cover Page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>9952151 - Statement - Condensed Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/CondensedConsolidatedBalanceSheets</Role>
      <ShortName>Condensed Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>9952152 - Statement - Condensed Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/CondensedConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Condensed Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>9952153 - Statement - Condensed Consolidated Statements of Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/CondensedConsolidatedStatementsofOperations</Role>
      <ShortName>Condensed Consolidated Statements of Operations</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>9952154 - Statement - Condensed Consolidated Statements of Operations (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/CondensedConsolidatedStatementsofOperationsParenthetical</Role>
      <ShortName>Condensed Consolidated Statements of Operations (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>9952155 - Statement - Condensed Consolidated Statements of Stockholders' Deficit</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/CondensedConsolidatedStatementsofStockholdersDeficit</Role>
      <ShortName>Condensed Consolidated Statements of Stockholders' Deficit</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>9952156 - Statement - Condensed Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/CondensedConsolidatedStatementsofCashFlows</Role>
      <ShortName>Condensed Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>9952157 - Disclosure - Nature of Business, Interim Financial Data and Basis of Presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/NatureofBusinessInterimFinancialDataandBasisofPresentation</Role>
      <ShortName>Nature of Business, Interim Financial Data and Basis of Presentation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>9952158 - Disclosure - Revenues</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/Revenues</Role>
      <ShortName>Revenues</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>9952159 - Disclosure - Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/IntangibleAssets</Role>
      <ShortName>Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>9952160 - Disclosure - Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/Debt</Role>
      <ShortName>Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>9952161 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/FairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>9952162 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>9952163 - Disclosure - Stockholders' Deficit</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/StockholdersDeficit</Role>
      <ShortName>Stockholders' Deficit</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>9952164 - Disclosure - Loss Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/LossPerShare</Role>
      <ShortName>Loss Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>9952165 - Disclosure - Reorganization items, net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/Reorganizationitemsnet</Role>
      <ShortName>Reorganization items, net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>9952166 - Disclosure - Liabilities Subject to Compromise</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/LiabilitiesSubjecttoCompromise</Role>
      <ShortName>Liabilities Subject to Compromise</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>9952167 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/CommitmentsandContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>9952168 - Disclosure - Condensed Combined Debtors' Financial Statements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/CondensedCombinedDebtorsFinancialStatements</Role>
      <ShortName>Condensed Combined Debtors' Financial Statements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>995445 - Disclosure - Insider Trading Arrangements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements</Role>
      <ShortName>Insider Trading Arrangements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>9955511 - Disclosure - Nature of Business, Interim Financial Data and Basis of Presentation (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/NatureofBusinessInterimFinancialDataandBasisofPresentationPolicies</Role>
      <ShortName>Nature of Business, Interim Financial Data and Basis of Presentation (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>9955512 - Disclosure - Nature of Business, Interim Financial Data and Basis of Presentation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/NatureofBusinessInterimFinancialDataandBasisofPresentationTables</Role>
      <ShortName>Nature of Business, Interim Financial Data and Basis of Presentation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/NatureofBusinessInterimFinancialDataandBasisofPresentation</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>9955513 - Disclosure - Revenues (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/RevenuesTables</Role>
      <ShortName>Revenues (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/Revenues</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>9955514 - Disclosure - Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/IntangibleAssetsTables</Role>
      <ShortName>Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/IntangibleAssets</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>9955515 - Disclosure - Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/DebtTables</Role>
      <ShortName>Debt (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/Debt</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>9955516 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/FairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/FairValueMeasurements</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>9955517 - Disclosure - Loss Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/LossPerShareTables</Role>
      <ShortName>Loss Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/LossPerShare</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>9955518 - Disclosure - Reorganization items, net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/ReorganizationitemsnetTables</Role>
      <ShortName>Reorganization items, net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/Reorganizationitemsnet</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>9955519 - Disclosure - Liabilities Subject to Compromise (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/LiabilitiesSubjecttoCompromiseTables</Role>
      <ShortName>Liabilities Subject to Compromise (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/LiabilitiesSubjecttoCompromise</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>9955520 - Disclosure - Condensed Combined Debtors' Financial Statements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/CondensedCombinedDebtorsFinancialStatementsTables</Role>
      <ShortName>Condensed Combined Debtors' Financial Statements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/CondensedCombinedDebtorsFinancialStatements</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>9955521 - Disclosure - Nature of Business, Interim Financial Data and Basis of Presentation - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/NatureofBusinessInterimFinancialDataandBasisofPresentationNarrativeDetails</Role>
      <ShortName>Nature of Business, Interim Financial Data and Basis of Presentation - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/NatureofBusinessInterimFinancialDataandBasisofPresentationTables</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>9955522 - Disclosure - Nature of Business, Interim Financial Data and Basis of Presentation - Schedule of Condensed Cash Flow Statement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/NatureofBusinessInterimFinancialDataandBasisofPresentationScheduleofCondensedCashFlowStatementDetails</Role>
      <ShortName>Nature of Business, Interim Financial Data and Basis of Presentation - Schedule of Condensed Cash Flow Statement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>9955523 - Disclosure - Revenues -Schedule of Disaggregated by Revenue Source (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/RevenuesScheduleofDisaggregatedbyRevenueSourceDetails</Role>
      <ShortName>Revenues -Schedule of Disaggregated by Revenue Source (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>9955524 - Disclosure - Revenues - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/RevenuesNarrativeDetails</Role>
      <ShortName>Revenues - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>9955525 - Disclosure - Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/IntangibleAssetsDetails</Role>
      <ShortName>Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/IntangibleAssetsTables</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>9955526 - Disclosure - Debt - Schedule of Short-term and Long-term Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/DebtScheduleofShorttermandLongtermDebtDetails</Role>
      <ShortName>Debt - Schedule of Short-term and Long-term Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>9955527 - Disclosure - Debt - 2026 Credit Agreement (Term Loan due 2026) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/Debt2026CreditAgreementTermLoandue2026Details</Role>
      <ShortName>Debt - 2026 Credit Agreement (Term Loan due 2026) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>9955528 - Disclosure - Debt - 2029 Credit Agreement (Term Loan Due 2029) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/Debt2029CreditAgreementTermLoanDue2029Details</Role>
      <ShortName>Debt - 2029 Credit Agreement (Term Loan Due 2029) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>9955529 - Disclosure - Debt - 2020 Revolving Credit Agreement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/Debt2020RevolvingCreditAgreementDetails</Role>
      <ShortName>Debt - 2020 Revolving Credit Agreement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>9955530 - Disclosure - Debt - 2026 Senior Notes (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.cumulus.com/role/Debt2026SeniorNotesDetails</Role>
      <ShortName>Debt - 2026 Senior Notes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>9955531 - Disclosure - Debt - 2029 Senior Notes (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.cumulus.com/role/Debt2029SeniorNotesDetails</Role>
      <ShortName>Debt - 2029 Senior Notes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>9955532 - Disclosure - Fair Value Measurements - Schedule of Gross Amounts and Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/FairValueMeasurementsScheduleofGrossAmountsandFairValueDetails</Role>
      <ShortName>Fair Value Measurements - Schedule of Gross Amounts and Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>9955533 - Disclosure - Fair Value Measurements - Schedule of Reconciliation of Fair Value Measurements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/FairValueMeasurementsScheduleofReconciliationofFairValueMeasurementsDetails</Role>
      <ShortName>Fair Value Measurements - Schedule of Reconciliation of Fair Value Measurements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>9955534 - Disclosure - Fair Value Measurements - Schedule of Fair Value Measurements of the Company's Investments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/FairValueMeasurementsScheduleofFairValueMeasurementsoftheCompanysInvestmentsDetails</Role>
      <ShortName>Fair Value Measurements - Schedule of Fair Value Measurements of the Company's Investments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>9955535 - Disclosure - Income Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/IncomeTaxesDetails</Role>
      <ShortName>Income Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/IncomeTaxes</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>9955536 - Disclosure - Stockholders' Deficit (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/StockholdersDeficitDetails</Role>
      <ShortName>Stockholders' Deficit (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/StockholdersDeficit</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>9955537 - Disclosure - Loss Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/LossPerShareDetails</Role>
      <ShortName>Loss Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/LossPerShareTables</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>9955538 - Disclosure - Reorganization items, net - Schedule of Reorganization, Chapter 11 (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/ReorganizationitemsnetScheduleofReorganizationChapter11Details</Role>
      <ShortName>Reorganization items, net - Schedule of Reorganization, Chapter 11 (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>9955539 - Disclosure - Reorganization items, net - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/ReorganizationitemsnetNarrativeDetails</Role>
      <ShortName>Reorganization items, net - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>9955540 - Disclosure - Liabilities Subject to Compromise (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/LiabilitiesSubjecttoCompromiseDetails</Role>
      <ShortName>Liabilities Subject to Compromise (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/LiabilitiesSubjecttoCompromiseTables</ParentRole>
      <Position>50</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>9955541 - Disclosure - Commitments and Contingencies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/CommitmentsandContingenciesDetails</Role>
      <ShortName>Commitments and Contingencies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cumulus.com/role/CommitmentsandContingencies</ParentRole>
      <Position>51</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>9955542 - Disclosure - Condensed Combined Debtors' Financial Statements - Schedule of Debtors' Balance Sheet (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/CondensedCombinedDebtorsFinancialStatementsScheduleofDebtorsBalanceSheetDetails</Role>
      <ShortName>Condensed Combined Debtors' Financial Statements - Schedule of Debtors' Balance Sheet (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>9955543 - Disclosure - Condensed Combined Debtors' Financial Statements - Schedule of Debtors' Statement of Operations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/CondensedCombinedDebtorsFinancialStatementsScheduleofDebtorsStatementofOperationsDetails</Role>
      <ShortName>Condensed Combined Debtors' Financial Statements - Schedule of Debtors' Statement of Operations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="cmls-20260630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>9955544 - Disclosure - Condensed Combined Debtors' Financial Statements - Schedule of Debtors' Statement of Cash Flows (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cumulus.com/role/CondensedCombinedDebtorsFinancialStatementsScheduleofDebtorsStatementofCashFlowsDetails</Role>
      <ShortName>Condensed Combined Debtors' Financial Statements - Schedule of Debtors' Statement of Cash Flows (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</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="10-Q" isDefinitelyFs="true" isUsgaap="true" original="cmls-20260630.htm">cmls-20260630.htm</File>
    <File>cmls-20260630.xsd</File>
    <File>cmls-20260630_cal.xml</File>
    <File>cmls-20260630_def.xml</File>
    <File>cmls-20260630_lab.xml</File>
    <File>cmls-20260630_pre.xml</File>
  </InputFiles>
  <SupplementalFiles>
    <File>cmls-20260630_g1.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="2">http://fasb.org/srt/2026</BaseTaxonomy>
    <BaseTaxonomy items="628">http://fasb.org/us-gaap/2026</BaseTaxonomy>
    <BaseTaxonomy items="29">http://xbrl.sec.gov/dei/2026</BaseTaxonomy>
    <BaseTaxonomy items="4">http://xbrl.sec.gov/ecd/2026</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
