<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.10.0.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>221</ContextCount>
  <ElementCount>295</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>55</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>6</UnitCount>
  <MyReports>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>00090 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>00100 - Statement - Balance Sheet</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/StatementBalanceSheet</Role>
      <ShortName>Balance Sheet</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>00105 - Statement - Balance Sheet (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/StatementBalanceSheetParenthetical</Role>
      <ShortName>Balance Sheet (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>00200 - Statement - Statement Of Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/StatementStatementOfOperations</Role>
      <ShortName>Statement Of Operations</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>00300 - Statement - Statement Of Comprehensive Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/StatementStatementOfComprehensiveLoss</Role>
      <ShortName>Statement Of Comprehensive Loss</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>00400 - Statement - Statement Of Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/StatementStatementOfStockholdersEquity</Role>
      <ShortName>Statement Of Stockholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>00600 - Statement - Statement Of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/StatementStatementOfCashFlows</Role>
      <ShortName>Statement Of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>10101 - Disclosure - Operations And Organization</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureOperationsAndOrganization</Role>
      <ShortName>Operations And Organization</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>10201 - Disclosure - Summary Of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary Of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>10301 - Disclosure - Marketable Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureMarketableSecurities</Role>
      <ShortName>Marketable Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>10401 - Disclosure - Prepaid Expenses And Other Current Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssets</Role>
      <ShortName>Prepaid Expenses And Other Current Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>10501 - Disclosure - Equipment, Net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureEquipmentNet</Role>
      <ShortName>Equipment, Net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>10601 - Disclosure - Accounts Payable And Accrued Expenses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureAccountsPayableAndAccruedExpenses</Role>
      <ShortName>Accounts Payable And Accrued Expenses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>10701 - Disclosure - Deferred Research And Development Arrangement</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureDeferredResearchAndDevelopmentArrangement</Role>
      <ShortName>Deferred Research And Development Arrangement</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>10801 - Disclosure - Other Liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureOtherLiabilities</Role>
      <ShortName>Other Liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>10901 - Disclosure - Net Loss Per Common Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureNetLossPerCommonShare</Role>
      <ShortName>Net Loss Per Common Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>11001 - Disclosure - Common Stock</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureCommonStock</Role>
      <ShortName>Common Stock</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>11101 - Disclosure - Stock-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureStockBasedCompensation</Role>
      <ShortName>Stock-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>11201 - Disclosure - Warrants</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureWarrants</Role>
      <ShortName>Warrants</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>11301 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureIncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>11401 - Disclosure - Collaboration Agreements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureCollaborationAgreements</Role>
      <ShortName>Collaboration Agreements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>11501 - Disclosure - Commitments And Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments And Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>11601 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureFairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>11701 - Disclosure - Select Quarterly Data</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureSelectQuarterlyData</Role>
      <ShortName>Select Quarterly Data</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>11801 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureSubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>20202 - Disclosure - Summary Of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary Of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>30203 - Disclosure - Summary Of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureSummaryOfSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary Of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>30303 - Disclosure - Marketable Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureMarketableSecuritiesTables</Role>
      <ShortName>Marketable Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureMarketableSecurities</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>30403 - Disclosure - Prepaid Expenses And Other Current Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssetsTables</Role>
      <ShortName>Prepaid Expenses And Other Current Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssets</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>30503 - Disclosure - Equipment, Net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureEquipmentNetTables</Role>
      <ShortName>Equipment, Net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureEquipmentNet</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>30603 - Disclosure - Accounts Payable And Accrued Expenses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureAccountsPayableAndAccruedExpensesTables</Role>
      <ShortName>Accounts Payable And Accrued Expenses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureAccountsPayableAndAccruedExpenses</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>30803 - Disclosure - Other Liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureOtherLiabilitiesTables</Role>
      <ShortName>Other Liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureOtherLiabilities</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>31003 - Disclosure - Common Stock (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureCommonStockTables</Role>
      <ShortName>Common Stock (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureCommonStock</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>31103 - Disclosure - Stock-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureStockBasedCompensationTables</Role>
      <ShortName>Stock-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureStockBasedCompensation</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>31203 - Disclosure - Warrants (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureWarrantsTables</Role>
      <ShortName>Warrants (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureWarrants</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>31303 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureIncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureIncomeTaxes</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>31503 - Disclosure - Commitments And Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureCommitmentsAndContingenciesTables</Role>
      <ShortName>Commitments And Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureCommitmentsAndContingencies</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>31603 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureFairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureFairValueMeasurements</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>31703 - Disclosure - Select Quarterly Data (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureSelectQuarterlyDataTables</Role>
      <ShortName>Select Quarterly Data (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureSelectQuarterlyData</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>40101 - Disclosure - Operations And Organization (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureOperationsAndOrganizationDetails</Role>
      <ShortName>Operations And Organization (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureOperationsAndOrganization</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>40201 - Disclosure - Summary Of Significant Accounting Policies (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureSummaryOfSignificantAccountingPoliciesNarrativeDetails</Role>
      <ShortName>Summary Of Significant Accounting Policies (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureSummaryOfSignificantAccountingPoliciesTables</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>40202 - Disclosure - Summary Of Significant Accounting Policies (Schedule Of Estimated Useful Lives) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureSummaryOfSignificantAccountingPoliciesScheduleOfEstimatedUsefulLivesDetails</Role>
      <ShortName>Summary Of Significant Accounting Policies (Schedule Of Estimated Useful Lives) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureSummaryOfSignificantAccountingPoliciesTables</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>40301 - Disclosure - Marketable Securities (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureMarketableSecuritiesNarrativeDetails</Role>
      <ShortName>Marketable Securities (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureMarketableSecuritiesTables</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>40302 - Disclosure - Marketable Securities (Schedule Of Cost And Fair Value Of Marketable Securities) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureMarketableSecuritiesScheduleOfCostAndFairValueOfMarketableSecuritiesDetails</Role>
      <ShortName>Marketable Securities (Schedule Of Cost And Fair Value Of Marketable Securities) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureMarketableSecuritiesTables</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>40401 - Disclosure - Prepaid Expenses And Other Current Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssetsDetails</Role>
      <ShortName>Prepaid Expenses And Other Current Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssetsTables</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>40501 - Disclosure - Equipment, Net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureEquipmentNetDetails</Role>
      <ShortName>Equipment, Net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureEquipmentNetTables</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>40601 - Disclosure - Accounts Payable And Accrued Expenses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureAccountsPayableAndAccruedExpensesDetails</Role>
      <ShortName>Accounts Payable And Accrued Expenses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureAccountsPayableAndAccruedExpensesTables</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>40701 - Disclosure - Deferred Research And Development Arrangement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureDeferredResearchAndDevelopmentArrangementDetails</Role>
      <ShortName>Deferred Research And Development Arrangement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureDeferredResearchAndDevelopmentArrangement</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>40801 - Disclosure - Other Liabilities (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureOtherLiabilitiesNarrativeDetails</Role>
      <ShortName>Other Liabilities (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureOtherLiabilitiesTables</ParentRole>
      <Position>49</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>40802 - Disclosure - Other Liabilities (Schedule Of Deferred Lease Incentive) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureOtherLiabilitiesScheduleOfDeferredLeaseIncentiveDetails</Role>
      <ShortName>Other Liabilities (Schedule Of Deferred Lease Incentive) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureOtherLiabilitiesTables</ParentRole>
      <Position>50</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>40901 - Disclosure - Net Loss Per Common Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureNetLossPerCommonShareDetails</Role>
      <ShortName>Net Loss Per Common Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureNetLossPerCommonShare</ParentRole>
      <Position>51</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>41001 - Disclosure - Common Stock (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureCommonStockNarrativeDetails</Role>
      <ShortName>Common Stock (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureCommonStockTables</ParentRole>
      <Position>52</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>41002 - Disclosure - Common Stock (Summary Of Allocation Of Proceeds From Offering) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureCommonStockSummaryOfAllocationOfProceedsFromOfferingDetails</Role>
      <ShortName>Common Stock (Summary Of Allocation Of Proceeds From Offering) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureCommonStockTables</ParentRole>
      <Position>53</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>41003 - Disclosure - Common Stock (Summary Of Issuances) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureCommonStockSummaryOfIssuancesDetails</Role>
      <ShortName>Common Stock (Summary Of Issuances) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureCommonStockTables</ParentRole>
      <Position>54</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>41101 - Disclosure - Stock-Based Compensation (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureStockBasedCompensationNarrativeDetails</Role>
      <ShortName>Stock-Based Compensation (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureStockBasedCompensationTables</ParentRole>
      <Position>55</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>41102 - Disclosure - Stock-Based Compensation (Summary Of Stock Compensation Expense) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureStockBasedCompensationSummaryOfStockCompensationExpenseDetails</Role>
      <ShortName>Stock-Based Compensation (Summary Of Stock Compensation Expense) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureStockBasedCompensationTables</ParentRole>
      <Position>56</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>41103 - Disclosure - Stock-Based Compensation (Schedule Of Assumptions Made In Calculating The Fair Value Of Options) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureStockBasedCompensationScheduleOfAssumptionsMadeInCalculatingFairValueOfOptionsDetails</Role>
      <ShortName>Stock-Based Compensation (Schedule Of Assumptions Made In Calculating The Fair Value Of Options) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureStockBasedCompensationTables</ParentRole>
      <Position>57</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>41104 - Disclosure - Stock-Based Compensation (Summary Of Share-Based Transactions ) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureStockBasedCompensationSummaryOfShareBasedTransactionsDetails</Role>
      <ShortName>Stock-Based Compensation (Summary Of Share-Based Transactions ) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureStockBasedCompensationTables</ParentRole>
      <Position>58</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>41106 - Disclosure - Stock-Based Compensation (Summary Of Unvested Shares) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureStockBasedCompensationSummaryOfUnvestedSharesDetails</Role>
      <ShortName>Stock-Based Compensation (Summary Of Unvested Shares) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureStockBasedCompensationTables</ParentRole>
      <Position>59</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>41107 - Disclosure - Stock-Based Compensation (Summary Of RSU Activity) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureStockBasedCompensationSummaryOfRsuActivityDetails</Role>
      <ShortName>Stock-Based Compensation (Summary Of RSU Activity) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureStockBasedCompensationTables</ParentRole>
      <Position>60</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>41201 - Disclosure - Warrants (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureWarrantsNarrativeDetails</Role>
      <ShortName>Warrants (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureWarrantsTables</ParentRole>
      <Position>61</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>41202 - Disclosure - Warrants (Summary Of Warrants Outstanding) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureWarrantsSummaryOfWarrantsOutstandingDetails</Role>
      <ShortName>Warrants (Summary Of Warrants Outstanding) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureWarrantsTables</ParentRole>
      <Position>62</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>41203 - Disclosure - Warrants (Summary Of Changes In Warrants Outstanding During The Period) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureWarrantsSummaryOfChangesInWarrantsOutstandingDuringPeriodDetails</Role>
      <ShortName>Warrants (Summary Of Changes In Warrants Outstanding During The Period) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureWarrantsTables</ParentRole>
      <Position>63</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>41204 - Disclosure - Warrants (Schedule Of Fair Value Of Warrants Issued) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureWarrantsScheduleOfFairValueOfWarrantsIssuedDetails</Role>
      <ShortName>Warrants (Schedule Of Fair Value Of Warrants Issued) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureWarrantsTables</ParentRole>
      <Position>64</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>41206 - Disclosure - Warrants (Schedule Of Assumptions Used In Calculating Fair Value Of Warrants) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureWarrantsScheduleOfAssumptionsUsedInCalculatingFairValueOfWarrantsDetails</Role>
      <ShortName>Warrants (Schedule Of Assumptions Used In Calculating Fair Value Of Warrants) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureWarrantsTables</ParentRole>
      <Position>65</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>41207 - Disclosure - Warrants (Schedule Of Unrealized Gain/(Loss) On Fair Value Of Warrants) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureWarrantsScheduleOfUnrealizedGainLossOnFairValueOfWarrantsDetails</Role>
      <ShortName>Warrants (Schedule Of Unrealized Gain/(Loss) On Fair Value Of Warrants) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureWarrantsTables</ParentRole>
      <Position>66</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>41301 - Disclosure - Income Taxes (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureIncomeTaxesNarrativeDetails</Role>
      <ShortName>Income Taxes (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureIncomeTaxesTables</ParentRole>
      <Position>67</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>41302 - Disclosure - Income Taxes (Schedule Of Deferred Tax Assets And Valuation Allowance) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureIncomeTaxesScheduleOfDeferredTaxAssetsAndValuationAllowanceDetails</Role>
      <ShortName>Income Taxes (Schedule Of Deferred Tax Assets And Valuation Allowance) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureIncomeTaxesTables</ParentRole>
      <Position>68</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>41501 - Disclosure - Commitments And Contingencies (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureCommitmentsAndContingenciesNarrativeDetails</Role>
      <ShortName>Commitments And Contingencies (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureCommitmentsAndContingenciesTables</ParentRole>
      <Position>69</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>41502 - Disclosure - Commitments and Contingencies (Schedule Of Future Rental Payments) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureCommitmentsAndContingenciesScheduleOfFutureRentalPaymentsDetails</Role>
      <ShortName>Commitments and Contingencies (Schedule Of Future Rental Payments) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>41602 - Disclosure - Fair Value Measurements (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureFairValueMeasurementsScheduleOfAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasisDetails</Role>
      <ShortName>Fair Value Measurements (Schedule Of Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureFairValueMeasurementsTables</ParentRole>
      <Position>71</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>41603 - Disclosure - Fair Value Measurements (Reconciliation Of Changes In The Fair Value Of Liabilities) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureFairValueMeasurementsReconciliationOfChangesInFairValueOfLiabilitiesDetails</Role>
      <ShortName>Fair Value Measurements (Reconciliation Of Changes In The Fair Value Of Liabilities) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureFairValueMeasurementsTables</ParentRole>
      <Position>72</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>41701 - Disclosure - Select Quarterly Data (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureSelectQuarterlyDataDetails</Role>
      <ShortName>Select Quarterly Data (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureSelectQuarterlyDataTables</ParentRole>
      <Position>73</Position>
    </Report>
    <Report instance="rnn-20181231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>41801 - Disclosure - Subsequent Events (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.rexahn.com/role/DisclosureSubsequentEventsDetails</Role>
      <ShortName>Subsequent Events (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.rexahn.com/role/DisclosureSubsequentEvents</ParentRole>
      <Position>74</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>rnn-20181231.xml</File>
    <File>rnn-20181231.xsd</File>
    <File>rnn-20181231_cal.xml</File>
    <File>rnn-20181231_def.xml</File>
    <File>rnn-20181231_lab.xml</File>
    <File>rnn-20181231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/us-gaap/2018-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2018-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2018-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
