<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.20.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>279</ContextCount>
  <ElementCount>560</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>77</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>15</UnitCount>
  <MyReports>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001001 - Document - COVER</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/COVER</Role>
      <ShortName>COVER</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001002 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1002003 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1003004 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1004005 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVELOSS</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1005006 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>2101101 - Disclosure - Nature of the Business and Basis of Presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/NatureoftheBusinessandBasisofPresentation</Role>
      <ShortName>Nature of the Business and Basis of Presentation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>2103102 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/SummaryofSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2109103 - Disclosure - Marketable Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/MarketableSecurities</Role>
      <ShortName>Marketable Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2116104 - Disclosure - Fair Value of Financial Assets and Liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/FairValueofFinancialAssetsandLiabilities</Role>
      <ShortName>Fair Value of Financial Assets and Liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2121105 - Disclosure - Prepaid Expenses and Other Current Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/PrepaidExpensesandOtherCurrentAssets</Role>
      <ShortName>Prepaid Expenses and Other Current Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2124106 - Disclosure - Equity Method Investment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/EquityMethodInvestment</Role>
      <ShortName>Equity Method Investment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2129107 - Disclosure - Accrued Expenses and Other Current Liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/AccruedExpensesandOtherCurrentLiabilities</Role>
      <ShortName>Accrued Expenses and Other Current Liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2132108 - Disclosure - Inventories</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/Inventories</Role>
      <ShortName>Inventories</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2135109 - Disclosure - Liability Related to Sale of Future Royalties, net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/LiabilityRelatedtoSaleofFutureRoyaltiesnet</Role>
      <ShortName>Liability Related to Sale of Future Royalties, net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2139110 - Disclosure - Mandatorily Redeemable Preferred Shares, net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/MandatorilyRedeemablePreferredSharesnet</Role>
      <ShortName>Mandatorily Redeemable Preferred Shares, net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2143111 - Disclosure - Warrants</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/Warrants</Role>
      <ShortName>Warrants</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2145112 - Disclosure - Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/ShareholdersEquity</Role>
      <ShortName>Shareholders' Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2149113 - Disclosure - Accumulated Other Comprehensive Income (Loss)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/AccumulatedOtherComprehensiveIncomeLoss</Role>
      <ShortName>Accumulated Other Comprehensive Income (Loss)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2152114 - Disclosure - Share-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/ShareBasedCompensation</Role>
      <ShortName>Share-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2158115 - Disclosure - Net Loss Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/NetLossPerShare</Role>
      <ShortName>Net Loss Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2162116 - Disclosure - License and Other Agreements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/LicenseandOtherAgreements</Role>
      <ShortName>License and Other Agreements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2171117 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2173118 - Disclosure - Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/Debt</Role>
      <ShortName>Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2178119 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/CommitmentsandContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2186120 - Disclosure - Related Party Transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/RelatedPartyTransactions</Role>
      <ShortName>Related Party Transactions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2204201 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/SummaryofSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/SummaryofSignificantAccountingPolicies</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2305301 - Disclosure - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/SummaryofSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/SummaryofSignificantAccountingPolicies</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2310302 - Disclosure - Marketable Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/MarketableSecuritiesTables</Role>
      <ShortName>Marketable Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/MarketableSecurities</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2317303 - Disclosure - Fair Value of Financial Assets and Liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/FairValueofFinancialAssetsandLiabilitiesTables</Role>
      <ShortName>Fair Value of Financial Assets and Liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/FairValueofFinancialAssetsandLiabilities</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2322304 - Disclosure - Prepaid Expenses and Other Current Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/PrepaidExpensesandOtherCurrentAssetsTables</Role>
      <ShortName>Prepaid Expenses and Other Current Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/PrepaidExpensesandOtherCurrentAssets</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2325305 - Disclosure - Equity Method Investment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/EquityMethodInvestmentTables</Role>
      <ShortName>Equity Method Investment (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/EquityMethodInvestment</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2330306 - Disclosure - Accrued Expenses and Other Current Liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/AccruedExpensesandOtherCurrentLiabilitiesTables</Role>
      <ShortName>Accrued Expenses and Other Current Liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/AccruedExpensesandOtherCurrentLiabilities</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2333307 - Disclosure - Inventories (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/InventoriesTables</Role>
      <ShortName>Inventories (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/Inventories</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2336308 - Disclosure - Liability Related to Sale of Future Royalties (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/LiabilityRelatedtoSaleofFutureRoyaltiesTables</Role>
      <ShortName>Liability Related to Sale of Future Royalties (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/LiabilityRelatedtoSaleofFutureRoyaltiesnet</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2340309 - Disclosure - Mandatorily Redeemable Preferred Shares, net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/MandatorilyRedeemablePreferredSharesnetTables</Role>
      <ShortName>Mandatorily Redeemable Preferred Shares, net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/MandatorilyRedeemablePreferredSharesnet</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2346310 - Disclosure - Shareholders' Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/ShareholdersEquityTables</Role>
      <ShortName>Shareholders' Equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/ShareholdersEquity</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2350311 - Disclosure - Accumulated Other Comprehensive Income (Loss) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/AccumulatedOtherComprehensiveIncomeLossTables</Role>
      <ShortName>Accumulated Other Comprehensive Income (Loss) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/AccumulatedOtherComprehensiveIncomeLoss</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2353312 - Disclosure - Share-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/ShareBasedCompensationTables</Role>
      <ShortName>Share-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/ShareBasedCompensation</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2359313 - Disclosure - Net Loss Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/NetLossPerShareTables</Role>
      <ShortName>Net Loss Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/NetLossPerShare</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2374314 - Disclosure - Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/DebtTables</Role>
      <ShortName>Debt (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/Debt</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2379315 - Disclosure - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/CommitmentsandContingenciesTables</Role>
      <ShortName>Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/CommitmentsandContingencies</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2402401 - Disclosure - Nature of the Business and Basis of Presentation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/NatureoftheBusinessandBasisofPresentationDetails</Role>
      <ShortName>Nature of the Business and Basis of Presentation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/NatureoftheBusinessandBasisofPresentation</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2406402 - Disclosure - Summary of Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/SummaryofSignificantAccountingPoliciesCashCashEquivalentsandRestrictedCashDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Cash, Cash Equivalents and Restricted Cash (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2407403 - Disclosure - Summary of Significant Accounting Policies - Estimated Future Amortization of Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/SummaryofSignificantAccountingPoliciesEstimatedFutureAmortizationofIntangibleAssetsDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Estimated Future Amortization of Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2408404 - Disclosure - Summary of Significant Accounting Policies - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2411405 - Disclosure - Marketable Securities - Amortized Cost and Fair Value of Debt Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/MarketableSecuritiesAmortizedCostandFairValueofDebtSecuritiesDetails</Role>
      <ShortName>Marketable Securities - Amortized Cost and Fair Value of Debt Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2412406 - Disclosure - Marketable Securities - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/MarketableSecuritiesNarrativeDetails</Role>
      <ShortName>Marketable Securities - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2413407 - Disclosure - Marketable Securities - Classification Debt Securities Available-for-Sale (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/MarketableSecuritiesClassificationDebtSecuritiesAvailableforSaleDetails</Role>
      <ShortName>Marketable Securities - Classification Debt Securities Available-for-Sale (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2414408 - Disclosure - Marketable Securities - Contractual Maturities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/MarketableSecuritiesContractualMaturitiesDetails</Role>
      <ShortName>Marketable Securities - Contractual Maturities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2415409 - Disclosure - Marketable Securities - Net Investment Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/MarketableSecuritiesNetInvestmentIncomeDetails</Role>
      <ShortName>Marketable Securities - Net Investment Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2418410 - Disclosure - Fair Value of Financial Assets and Liabilities - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/FairValueofFinancialAssetsandLiabilitiesNarrativeDetails</Role>
      <ShortName>Fair Value of Financial Assets and Liabilities - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2419411 - Disclosure - Fair Value of Financial Assets and Liabilities - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/FairValueofFinancialAssetsandLiabilitiesFinancialAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails</Role>
      <ShortName>Fair Value of Financial Assets and Liabilities - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2420412 - Disclosure - Fair Value of Financial Assets and Liabilities - Roll Forward of Aggregate Fair Value Determined by Level 3 Inputs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/FairValueofFinancialAssetsandLiabilitiesRollForwardofAggregateFairValueDeterminedbyLevel3InputsDetails</Role>
      <ShortName>Fair Value of Financial Assets and Liabilities - Roll Forward of Aggregate Fair Value Determined by Level 3 Inputs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2423413 - Disclosure - Prepaid Expenses and Other Current Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/PrepaidExpensesandOtherCurrentAssetsDetails</Role>
      <ShortName>Prepaid Expenses and Other Current Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/PrepaidExpensesandOtherCurrentAssetsTables</ParentRole>
      <Position>55</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2426414 - Disclosure - Equity Method Investment - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/EquityMethodInvestmentNarrativeDetails</Role>
      <ShortName>Equity Method Investment - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2427415 - Disclosure - Equity Method Investment - Expense and Carrying Amount of Investment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/EquityMethodInvestmentExpenseandCarryingAmountofInvestmentDetails</Role>
      <ShortName>Equity Method Investment - Expense and Carrying Amount of Investment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>2428416 - Disclosure - Equity Method Investment - Roll-forward of Carrying Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/EquityMethodInvestmentRollforwardofCarryingValueDetails</Role>
      <ShortName>Equity Method Investment - Roll-forward of Carrying Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>2431417 - Disclosure - Accrued Expenses and Other Current Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/AccruedExpensesandOtherCurrentLiabilitiesDetails</Role>
      <ShortName>Accrued Expenses and Other Current Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/AccruedExpensesandOtherCurrentLiabilitiesTables</ParentRole>
      <Position>59</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>2434418 - Disclosure - Inventories (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/InventoriesDetails</Role>
      <ShortName>Inventories (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/InventoriesTables</ParentRole>
      <Position>60</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>2437419 - Disclosure - Liability Related to Sale of Future Royalties, net - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/LiabilityRelatedtoSaleofFutureRoyaltiesnetNarrativeDetails</Role>
      <ShortName>Liability Related to Sale of Future Royalties, net - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/LiabilityRelatedtoSaleofFutureRoyaltiesnet</ParentRole>
      <Position>61</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>2438420 - Disclosure - Liability Related to Sale of Future Royalties, net - Activity within Liability Account (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/LiabilityRelatedtoSaleofFutureRoyaltiesnetActivitywithinLiabilityAccountDetails</Role>
      <ShortName>Liability Related to Sale of Future Royalties, net - Activity within Liability Account (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>2441421 - Disclosure - Mandatorily Redeemable Preferred Shares, net - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/MandatorilyRedeemablePreferredSharesnetNarrativeDetails</Role>
      <ShortName>Mandatorily Redeemable Preferred Shares, net - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>2442422 - Disclosure - Mandatorily Redeemable Preferred Shares, net - Activity Within the Preferred Share Liability (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/MandatorilyRedeemablePreferredSharesnetActivityWithinthePreferredShareLiabilityDetails</Role>
      <ShortName>Mandatorily Redeemable Preferred Shares, net - Activity Within the Preferred Share Liability (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>2444423 - Disclosure - Warrants - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/WarrantsNarrativeDetails</Role>
      <ShortName>Warrants - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>2447424 - Disclosure - Shareholders' Equity - Changes in Shareholders' Equity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/ShareholdersEquityChangesinShareholdersEquityDetails</Role>
      <ShortName>Shareholders' Equity - Changes in Shareholders' Equity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>2448425 - Disclosure - Shareholders' Equity - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/ShareholdersEquityNarrativeDetails</Role>
      <ShortName>Shareholders' Equity - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>2451426 - Disclosure - Accumulated Other Comprehensive Income (Loss) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/AccumulatedOtherComprehensiveIncomeLossDetails</Role>
      <ShortName>Accumulated Other Comprehensive Income (Loss) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/AccumulatedOtherComprehensiveIncomeLossTables</ParentRole>
      <Position>68</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>2454427 - Disclosure - Share-Based Compensation - Non-Cash Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/ShareBasedCompensationNonCashExpenseDetails</Role>
      <ShortName>Share-Based Compensation - Non-Cash Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>2455428 - Disclosure - Share-Based Compensation - Stock Options (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/ShareBasedCompensationStockOptionsDetails</Role>
      <ShortName>Share-Based Compensation - Stock Options (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>2456429 - Disclosure - Share-Based Compensation - Restricted Share Units (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/ShareBasedCompensationRestrictedShareUnitsDetails</Role>
      <ShortName>Share-Based Compensation - Restricted Share Units (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>2457430 - Disclosure - Share-Based Compensation - Employee Stock Purchase Plan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/ShareBasedCompensationEmployeeStockPurchasePlanDetails</Role>
      <ShortName>Share-Based Compensation - Employee Stock Purchase Plan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>2460431 - Disclosure - Net Loss Per Share - Calculation of Basic and Diluted Net Loss per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/NetLossPerShareCalculationofBasicandDilutedNetLossperShareDetails</Role>
      <ShortName>Net Loss Per Share - Calculation of Basic and Diluted Net Loss per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>2461432 - Disclosure - Net Loss Per Share - Antidilutive Securities Excluded from Computation of Net Loss per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/NetLossPerShareAntidilutiveSecuritiesExcludedfromComputationofNetLossperShareDetails</Role>
      <ShortName>Net Loss Per Share - Antidilutive Securities Excluded from Computation of Net Loss per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>2463433 - Disclosure - License and Other Agreements - Amendment to License Agreement with Yale (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/LicenseandOtherAgreementsAmendmenttoLicenseAgreementwithYaleDetails</Role>
      <ShortName>License and Other Agreements - Amendment to License Agreement with Yale (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>2464434 - Disclosure - License and Other Agreements - ALS Biopharma Agreement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/LicenseandOtherAgreementsALSBiopharmaAgreementDetails</Role>
      <ShortName>License and Other Agreements - ALS Biopharma Agreement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>2465435 - Disclosure - License and Other Agreements - Catalent Agreement for Rimegepant (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/LicenseandOtherAgreementsCatalentAgreementforRimegepantDetails</Role>
      <ShortName>License and Other Agreements - Catalent Agreement for Rimegepant (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>2466436 - Disclosure - License and Other Agreements - Rutgers Agreement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/LicenseandOtherAgreementsRutgersAgreementDetails</Role>
      <ShortName>License and Other Agreements - Rutgers Agreement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>2467437 - Disclosure - License and Other Agreements - BMS Agreement and Amendment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/LicenseandOtherAgreementsBMSAgreementandAmendmentDetails</Role>
      <ShortName>License and Other Agreements - BMS Agreement and Amendment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>2468438 - Disclosure - License and Other Agreements - AstraZeneca Agreement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/LicenseandOtherAgreementsAstraZenecaAgreementDetails</Role>
      <ShortName>License and Other Agreements - AstraZeneca Agreement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>2469439 - Disclosure - License and Other Agreements - Revenue Participation Rights (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/LicenseandOtherAgreementsRevenueParticipationRightsDetails</Role>
      <ShortName>License and Other Agreements - Revenue Participation Rights (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>2470440 - Disclosure - License and Other Agreements - Fox Chase Chemical Diversity Center Agreement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/LicenseandOtherAgreementsFoxChaseChemicalDiversityCenterAgreementDetails</Role>
      <ShortName>License and Other Agreements - Fox Chase Chemical Diversity Center Agreement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>2472441 - Disclosure - Income Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/IncomeTaxesDetails</Role>
      <ShortName>Income Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.biohavenpharma.com/role/IncomeTaxes</ParentRole>
      <Position>83</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>2475442 - Disclosure - Debt - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/DebtNarrativeDetails</Role>
      <ShortName>Debt - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>2476443 - Disclosure - Debt - Summary of borrowings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/DebtSummaryofborrowingsDetails</Role>
      <ShortName>Debt - Summary of borrowings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>85</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>2477444 - Disclosure - Debt - Repayments of debt principal (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/DebtRepaymentsofdebtprincipalDetails</Role>
      <ShortName>Debt - Repayments of debt principal (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>86</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>2480445 - Disclosure - Commitments and Contingencies - Lease Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/CommitmentsandContingenciesLeaseAssetsandLiabilitiesDetails</Role>
      <ShortName>Commitments and Contingencies - Lease Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>87</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>2481446 - Disclosure - Commitments and Contingencies - Lease Costs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/CommitmentsandContingenciesLeaseCostsDetails</Role>
      <ShortName>Commitments and Contingencies - Lease Costs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>88</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>2482447 - Disclosure - Commitments and Contingencies - Supplemental Cash Flow Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/CommitmentsandContingenciesSupplementalCashFlowInformationDetails</Role>
      <ShortName>Commitments and Contingencies - Supplemental Cash Flow Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>89</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>2483448 - Disclosure - Commitments and Contingencies - Maturities of Lease Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/CommitmentsandContingenciesMaturitiesofLeaseLiabilitiesDetails</Role>
      <ShortName>Commitments and Contingencies - Maturities of Lease Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>90</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>2484449 - Disclosure - Commitments and Contingencies - Reconciliation of Lease Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/CommitmentsandContingenciesReconciliationofLeaseLiabilitiesDetails</Role>
      <ShortName>Commitments and Contingencies - Reconciliation of Lease Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>91</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>2485450 - Disclosure - Commitments and Contingencies - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/CommitmentsandContingenciesNarrativeDetails</Role>
      <ShortName>Commitments and Contingencies - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>92</Position>
    </Report>
    <Report instance="bhvn-20200930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R93.htm</HtmlFileName>
      <LongName>2487451 - Disclosure - Related Party Transactions - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.biohavenpharma.com/role/RelatedPartyTransactionsNarrativeDetails</Role>
      <ShortName>Related Party Transactions - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>93</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" original="bhvn-20200930.htm">bhvn-20200930.htm</File>
    <File>a2020amendmentto2018fundin.htm</File>
    <File>a2020augustfinancingagreem.htm</File>
    <File>a2020augustfundingagre.htm</File>
    <File>a2020augustseriesbpreferre.htm</File>
    <File>a2020q3bhvn10-qexh311.htm</File>
    <File>a2020q3bhvn10-qexh312.htm</File>
    <File>a2020q3bhvn10-qexh321.htm</File>
    <File>bhvn-20200930.xsd</File>
    <File>bhvn-20200930_cal.xml</File>
    <File>bhvn-20200930_def.xml</File>
    <File>bhvn-20200930_lab.xml</File>
    <File>bhvn-20200930_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/srt/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2020-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
