<?xml version='1.0' encoding='UTF-8'?>
<FilingSummary>
  <Version>3.2.0.727</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>103</ContextCount>
  <ElementCount>222</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>48</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>4</UnitCount>
  <MyReports>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001000 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/DocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001000 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/ConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1001501 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/ConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1003000 - Statement - Consolidated Statements of Operations and Comprehensive Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/ConsolidatedStatementsOfOperationsAndComprehensiveLoss</Role>
      <ShortName>Consolidated Statements of Operations and Comprehensive Loss</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1005000 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/ConsolidatedStatementsOfCashFlows</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1005501 - Statement - Consolidated Statements of Cash Flows (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/ConsolidatedStatementsOfCashFlowsParenthetical</Role>
      <ShortName>Consolidated Statements of Cash Flows (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>2101100 - Disclosure - Description of Business</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/DescriptionOfBusiness</Role>
      <ShortName>Description of Business</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>2102100 - Disclosure - Net (Loss) Income Per Share (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.agenusbio.com/role/NetLossIncomePerShareNotes</Role>
      <ShortName>Net (Loss) Income Per Share (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2103100 - Disclosure - Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/Debt</Role>
      <ShortName>Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2104100 - Disclosure - Collaborations (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.agenusbio.com/role/CollaborationsNotes</Role>
      <ShortName>Collaborations (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2105100 - Disclosure - Goodwill and acquired intangibles (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.agenusbio.com/role/GoodwillAndAcquiredIntangiblesNotes</Role>
      <ShortName>Goodwill and acquired intangibles (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2106100 - Disclosure - Investments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/Investments</Role>
      <ShortName>Investments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2107100 - Disclosure - Share-Based Compensation Plans (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.agenusbio.com/role/ShareBasedCompensationPlansNotes</Role>
      <ShortName>Share-Based Compensation Plans (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2108100 - Disclosure - Accrued and Other Current Liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/AccruedAndOtherCurrentLiabilities</Role>
      <ShortName>Accrued and Other Current Liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2109100 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/FairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2110100 - Disclosure - Benefit Plans (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.agenusbio.com/role/BenefitPlansNotes</Role>
      <ShortName>Benefit Plans (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2112100 - Disclosure - Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/Equity</Role>
      <ShortName>Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2114100 - Disclosure - Asset Purchase Agreement</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/AssetPurchaseAgreement</Role>
      <ShortName>Asset Purchase Agreement</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2118100 - Disclosure - Recent Accounting Pronouncements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/RecentAccountingPronouncements</Role>
      <ShortName>Recent Accounting Pronouncements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2302301 - Disclosure - Net (Loss) Income Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/NetLossIncomePerShareTables</Role>
      <ShortName>Net (Loss) Income Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/NetLossIncomePerShareNotes</ParentRole>
      <Position>20</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2305301 - Disclosure - Goodwill and acquired intangibles (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/GoodwillAndAcquiredIntangiblesTables</Role>
      <ShortName>Goodwill and acquired intangibles (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/GoodwillAndAcquiredIntangiblesNotes</ParentRole>
      <Position>21</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2306301 - Disclosure - Investments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/InvestmentsTables</Role>
      <ShortName>Investments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/Investments</ParentRole>
      <Position>22</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2307301 - Disclosure - Share-Based Compensation Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/ShareBasedCompensationPlansTables</Role>
      <ShortName>Share-Based Compensation Plans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/ShareBasedCompensationPlansNotes</ParentRole>
      <Position>23</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2308301 - Disclosure - Accrued and Other Current Liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/AccruedAndOtherCurrentLiabilitiesTables</Role>
      <ShortName>Accrued and Other Current Liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/AccruedAndOtherCurrentLiabilities</ParentRole>
      <Position>24</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2309301 - Disclosure - Fair Value Measurements Fair value measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/FairValueMeasurementsFairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements Fair value measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2401401 - Disclosure - Description of Business (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/DescriptionOfBusinessDetails</Role>
      <ShortName>Description of Business (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/DescriptionOfBusiness</ParentRole>
      <Position>26</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2402402 - Disclosure - Net (Loss) Income Per Share Antidilutive securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/NetLossIncomePerShareAntidilutiveSecuritiesDetails</Role>
      <ShortName>Net (Loss) Income Per Share Antidilutive securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/NetLossIncomePerShareTables</ParentRole>
      <Position>27</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2403401 - Disclosure - Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/DebtDetails</Role>
      <ShortName>Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/Debt</ParentRole>
      <Position>28</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2404401 - Disclosure - Collaborations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/CollaborationsDetails</Role>
      <ShortName>Collaborations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/CollaborationsNotes</ParentRole>
      <Position>29</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2405402 - Disclosure - Goodwill and acquired intangibles (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/GoodwillAndAcquiredIntangiblesNarrativeDetails</Role>
      <ShortName>Goodwill and acquired intangibles (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/GoodwillAndAcquiredIntangiblesTables</ParentRole>
      <Position>30</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2405403 - Disclosure - Goodwill and acquired intangibles (Schedule of Changes in Goodwill) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/GoodwillAndAcquiredIntangiblesScheduleOfChangesInGoodwillDetails</Role>
      <ShortName>Goodwill and acquired intangibles (Schedule of Changes in Goodwill) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/GoodwillAndAcquiredIntangiblesTables</ParentRole>
      <Position>31</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2405404 - Disclosure - Goodwill and acquired intangibles (Acquired Finite-Lived Intangible Assets) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/GoodwillAndAcquiredIntangiblesAcquiredFiniteLivedIntangibleAssetsDetails</Role>
      <ShortName>Goodwill and acquired intangibles (Acquired Finite-Lived Intangible Assets) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/GoodwillAndAcquiredIntangiblesTables</ParentRole>
      <Position>32</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2406402 - Disclosure - Investments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/InvestmentsDetails</Role>
      <ShortName>Investments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/InvestmentsTables</ParentRole>
      <Position>33</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2407402 - Disclosure - Share-Based Compensation Plans (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/ShareBasedCompensationPlansNarrativeDetails</Role>
      <ShortName>Share-Based Compensation Plans (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/ShareBasedCompensationPlansTables</ParentRole>
      <Position>34</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2407403 - Disclosure - Share-Based Compensation Plans (Schedule Of Stock Option Activity) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/ShareBasedCompensationPlansScheduleOfStockOptionActivityDetails</Role>
      <ShortName>Share-Based Compensation Plans (Schedule Of Stock Option Activity) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/ShareBasedCompensationPlansTables</ParentRole>
      <Position>35</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2407404 - Disclosure - Share-Based Compensation Plans (Summary Of Nonvested Stock Activity) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/ShareBasedCompensationPlansSummaryOfNonvestedStockActivityDetails</Role>
      <ShortName>Share-Based Compensation Plans (Summary Of Nonvested Stock Activity) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/ShareBasedCompensationPlansTables</ParentRole>
      <Position>36</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2407405 - Disclosure - Share-Based Compensation Plans (Schedule Of Share-Based Compensation Expense) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/ShareBasedCompensationPlansScheduleOfShareBasedCompensationExpenseDetails</Role>
      <ShortName>Share-Based Compensation Plans (Schedule Of Share-Based Compensation Expense) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/ShareBasedCompensationPlansTables</ParentRole>
      <Position>37</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2408402 - Disclosure - Accrued and Other Current Liabilities Schedule of accrued liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/AccruedAndOtherCurrentLiabilitiesScheduleOfAccruedLiabilitiesDetails</Role>
      <ShortName>Accrued and Other Current Liabilities Schedule of accrued liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2408403 - Disclosure - Schedule of Other Current Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/ScheduleOfOtherCurrentLiabilitiesDetails</Role>
      <ShortName>Schedule of Other Current Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2409402 - Disclosure - Fair Value Measurements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/FairValueMeasurementsDetails</Role>
      <ShortName>Fair Value Measurements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/FairValueMeasurementsFairValueMeasurementsTables</ParentRole>
      <Position>40</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2409403 - Schedule - Fair Value Measurements (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/FairValueMeasurementsNarrativeDetails</Role>
      <ShortName>Fair Value Measurements (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/FairValueMeasurementsFairValueMeasurementsTables</ParentRole>
      <Position>41</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2409404 - Disclosure - Fair Value Measurements Asset and Liabilities Measured at Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/FairValueMeasurementsAssetAndLiabilitiesMeasuredAtFairValueDetails</Role>
      <ShortName>Fair Value Measurements Asset and Liabilities Measured at Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2410401 - Disclosure - Benefit Plans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/BenefitPlansDetails</Role>
      <ShortName>Benefit Plans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/BenefitPlansNotes</ParentRole>
      <Position>43</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2412401 - Disclosure - Equity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/EquityDetails</Role>
      <ShortName>Equity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/Equity</ParentRole>
      <Position>44</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2414401 - Disclosure - Asset Purchase Agreement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.agenusbio.com/role/AssetPurchaseAgreementDetails</Role>
      <ShortName>Asset Purchase Agreement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.agenusbio.com/role/AssetPurchaseAgreement</ParentRole>
      <Position>45</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <Logs>
    <Log type="Info">In ''Consolidated Balance Sheets'', column(s) 3, 4 are contained in other reports, so were removed by flow through suppression.</Log>
    <Log type="Info">In ''Consolidated Balance Sheets (Parenthetical)'', column(s) 7 are contained in other reports, so were removed by flow through suppression.</Log>
    <Log type="Info">In ''Consolidated Statements of Cash Flows'', column(s) 1, 2 are contained in other reports, so were removed by flow through suppression.</Log>
  </Logs>
  <InputFiles>
    <File>agen-20150630.xml</File>
    <File>agen-20150630_cal.xml</File>
    <File>agen-20150630_def.xml</File>
    <File>agen-20150630_lab.xml</File>
    <File>agen-20150630_pre.xml</File>
    <File>agen-20150630.xsd</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies/>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>

