<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.20.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>526</ContextCount>
  <ElementCount>509</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>200</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>4</UnitCount>
  <MyReports>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>000 - Document - Document And Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-document-and-entity-information</Role>
      <ShortName>Document And Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>001 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-consolidated-balance-sheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>002 - Statement - Consolidated Balance Sheets (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-consolidated-balance-sheets-parentheticals</Role>
      <ShortName>Consolidated Balance Sheets (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>003 - Statement - Consolidated Statements of Operations and Comprehensive Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-consolidated-statements-of-operations-and-comprehensive-loss</Role>
      <ShortName>Consolidated Statements of Operations and Comprehensive Loss</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>004 - Statement - Consolidated Statement of Stockholders' Equity (Deficit)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-consolidated-statement-of-stockholders-equity-deficit</Role>
      <ShortName>Consolidated Statement of Stockholders' Equity (Deficit)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>005 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-consolidated-statements-of-cash-flows</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>006 - Disclosure - Note 1 - Business and Organization</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-1-business-and-organization</Role>
      <ShortName>Note 1 - Business and Organization</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>007 - Disclosure - Note 2 - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-2-summary-of-significant-accounting-policies</Role>
      <ShortName>Note 2 - Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>008 - Disclosure - Note 3 - Lincoln Park Financing</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-3-lincoln-park-financing</Role>
      <ShortName>Note 3 - Lincoln Park Financing</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>009 - Disclosure - Note 4 - Debt Obligations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-4-debt-obligations</Role>
      <ShortName>Note 4 - Debt Obligations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>010 - Disclosure - Note 5 - Share-based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-5-sharebased-compensation</Role>
      <ShortName>Note 5 - Share-based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>011 - Disclosure - Note 6 - Warrants</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-6-warrants</Role>
      <ShortName>Note 6 - Warrants</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>012 - Disclosure - Note 7 - Accounts Payable and Accrued Expenses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-7-accounts-payable-and-accrued-expenses</Role>
      <ShortName>Note 7 - Accounts Payable and Accrued Expenses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>013 - Disclosure - Note 8 - Provision for Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-8-provision-for-income-taxes-</Role>
      <ShortName>Note 8 - Provision for Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>014 - Disclosure - Note 9 - Noncontrolling Interest - Clyra Medical</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-9-noncontrolling-interest-clyra-medical</Role>
      <ShortName>Note 9 - Noncontrolling Interest - Clyra Medical</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>015 - Disclosure - Note 10 - BioLargo Engineering, Science and Technologies, LLC</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-10-biolargo-engineering-science-and-technologies-llc</Role>
      <ShortName>Note 10 - BioLargo Engineering, Science and Technologies, LLC</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>016 - Disclosure - Note 11 - Business Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-11-business-segment-information</Role>
      <ShortName>Note 11 - Business Segment Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>017 - Disclosure - Note 12 - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-12-commitments-and-contingencies</Role>
      <ShortName>Note 12 - Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>018 - Disclosure - Note 13 - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-13-subsequent-events</Role>
      <ShortName>Note 13 - Subsequent Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>019 - Disclosure - Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-significant-accounting-policies-policies</Role>
      <ShortName>Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-2-summary-of-significant-accounting-policies</ParentRole>
      <Position>20</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>020 - Disclosure - Note 2 - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-2-summary-of-significant-accounting-policies-tables</Role>
      <ShortName>Note 2 - Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-2-summary-of-significant-accounting-policies</ParentRole>
      <Position>21</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>021 - Disclosure - Note 3 - Lincoln Park Financing (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-3-lincoln-park-financing-tables</Role>
      <ShortName>Note 3 - Lincoln Park Financing (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-3-lincoln-park-financing</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>022 - Disclosure - Note 4 - Debt Obligations (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-4-debt-obligations-tables</Role>
      <ShortName>Note 4 - Debt Obligations (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-4-debt-obligations</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>023 - Disclosure - Note 5 - Share-based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-5-sharebased-compensation-tables</Role>
      <ShortName>Note 5 - Share-based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-5-sharebased-compensation</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>024 - Disclosure - Note 6 - Warrants (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-6-warrants-tables</Role>
      <ShortName>Note 6 - Warrants (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-6-warrants</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>025 - Disclosure - Note 7 - Accounts Payable and Accrued Expenses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-7-accounts-payable-and-accrued-expenses-tables</Role>
      <ShortName>Note 7 - Accounts Payable and Accrued Expenses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-7-accounts-payable-and-accrued-expenses</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>026 - Disclosure - Note 9 - Noncontrolling Interest - Clyra Medical (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-9-noncontrolling-interest-clyra-medical-tables</Role>
      <ShortName>Note 9 - Noncontrolling Interest - Clyra Medical (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-9-noncontrolling-interest-clyra-medical</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>027 - Disclosure - Note 11 - Business Segment Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-11-business-segment-information-tables</Role>
      <ShortName>Note 11 - Business Segment Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-11-business-segment-information</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>028 - Disclosure - Note 12 - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-12-commitments-and-contingencies-tables</Role>
      <ShortName>Note 12 - Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-12-commitments-and-contingencies</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>029 - Disclosure - Note 1 - Business and Organization (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-1-business-and-organization-details-textual</Role>
      <ShortName>Note 1 - Business and Organization (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-1-business-and-organization</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>030 - Disclosure - Note 2 - Summary of Significant Accounting Policies (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-2-summary-of-significant-accounting-policies-details-textual</Role>
      <ShortName>Note 2 - Summary of Significant Accounting Policies (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-2-summary-of-significant-accounting-policies-tables</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>031 - Disclosure - Note 2 - Summary of Significant Accounting Policies - Summary of Cash Balances (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-2-summary-of-significant-accounting-policies-summary-of-cash-balances-details</Role>
      <ShortName>Note 2 - Summary of Significant Accounting Policies - Summary of Cash Balances (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>032 - Disclosure - Note 2 - Summary of Significant Accounting Policies - Credit Concentration (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-2-summary-of-significant-accounting-policies-credit-concentration-details</Role>
      <ShortName>Note 2 - Summary of Significant Accounting Policies - Credit Concentration (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>033 - Disclosure - Note 2 - Summary of Significant Accounting Policies - Inventory (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-2-summary-of-significant-accounting-policies-inventory-details</Role>
      <ShortName>Note 2 - Summary of Significant Accounting Policies - Inventory (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-2-summary-of-significant-accounting-policies-tables</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>034 - Disclosure - Note 2 - Summary of Significant Accounting Policies - Stock Options, Valuation Assumptions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-2-summary-of-significant-accounting-policies-stock-options-valuation-assumptions-details</Role>
      <ShortName>Note 2 - Summary of Significant Accounting Policies - Stock Options, Valuation Assumptions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>035 - Disclosure - Note 3 - Lincoln Park Financing (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-3-lincoln-park-financing-details-textual</Role>
      <ShortName>Note 3 - Lincoln Park Financing (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-3-lincoln-park-financing-tables</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>036 - Disclosure - Note 3 - Lincoln Park Financing - Purchase Agreement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-3-lincoln-park-financing-purchase-agreement-details</Role>
      <ShortName>Note 3 - Lincoln Park Financing - Purchase Agreement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>037 - Disclosure - Note 4 - Debt Obligations (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-4-debt-obligations-details-textual</Role>
      <ShortName>Note 4 - Debt Obligations (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-4-debt-obligations-tables</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>038 - Disclosure - Note 4 - Debt Obligations - Schedule of Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-4-debt-obligations-schedule-of-debt-details</Role>
      <ShortName>Note 4 - Debt Obligations - Schedule of Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>039 - Disclosure - Note 4 - Debt Obligations - Early Conversion of Unit Notes (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-4-debt-obligations-early-conversion-of-unit-notes-details</Role>
      <ShortName>Note 4 - Debt Obligations - Early Conversion of Unit Notes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>040 - Disclosure - Note 5 - Share-based Compensation (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-5-sharebased-compensation-details-textual</Role>
      <ShortName>Note 5 - Share-based Compensation (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-5-sharebased-compensation-tables</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>041 - Disclosure - Note 5 - Share-based Compensation - Stock Options (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-5-sharebased-compensation-stock-options-details</Role>
      <ShortName>Note 5 - Share-based Compensation - Stock Options (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>042 - Disclosure - Note 5 - Share-based Compensation - Stock Options Issued Under the 2007 Equity Incentive Plan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-5-sharebased-compensation-stock-options-issued-under-the-2007-equity-incentive-plan-details</Role>
      <ShortName>Note 5 - Share-based Compensation - Stock Options Issued Under the 2007 Equity Incentive Plan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>043 - Disclosure - Note 6 - Warrants (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-6-warrants-details-textual</Role>
      <ShortName>Note 6 - Warrants (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-6-warrants-tables</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>044 - Disclosure - Note 6 - Warrants - Warrants Outstanding (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-6-warrants-warrants-outstanding-details</Role>
      <ShortName>Note 6 - Warrants - Warrants Outstanding (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>045 - Disclosure - Note 6 - Warrants - Assumptions Used to Determine Fair Value of Warrants (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-6-warrants-assumptions-used-to-determine-fair-value-of-warrants-details</Role>
      <ShortName>Note 6 - Warrants - Assumptions Used to Determine Fair Value of Warrants (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>046 - Disclosure - Note 7 - Accounts Payable and Accrued Expenses - Summary of Accounts Payable and Accrued Expenses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-7-accounts-payable-and-accrued-expenses-summary-of-accounts-payable-and-accrued-expenses-details</Role>
      <ShortName>Note 7 - Accounts Payable and Accrued Expenses - Summary of Accounts Payable and Accrued Expenses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>047 - Disclosure - Note 8 - Provision for Income Taxes (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-8-provision-for-income-taxes-details-textual</Role>
      <ShortName>Note 8 - Provision for Income Taxes (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-8-provision-for-income-taxes-</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>048 - Disclosure - Note 9 - Noncontrolling Interest - Clyra Medical (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-9-noncontrolling-interest-clyra-medical-details-textual</Role>
      <ShortName>Note 9 - Noncontrolling Interest - Clyra Medical (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-9-noncontrolling-interest-clyra-medical-tables</ParentRole>
      <Position>49</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>049 - Disclosure - Note 9 - Noncontrolling Interest - Clyra Medical Common and Preferred Shares Outstanding (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-9-noncontrolling-interest-clyra-medical-common-and-preferred-shares-outstanding-details</Role>
      <ShortName>Note 9 - Noncontrolling Interest - Clyra Medical Common and Preferred Shares Outstanding (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>050 - Disclosure - Note 10 - BioLargo Engineering, Science and Technologies, LLC (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-10-biolargo-engineering-science-and-technologies-llc-details-textual</Role>
      <ShortName>Note 10 - BioLargo Engineering, Science and Technologies, LLC (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-10-biolargo-engineering-science-and-technologies-llc</ParentRole>
      <Position>51</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>051 - Disclosure - Note 11 - Business Segment Information (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-11-business-segment-information-details-textual</Role>
      <ShortName>Note 11 - Business Segment Information (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-11-business-segment-information-tables</ParentRole>
      <Position>52</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>052 - Disclosure - Note 11 - Business Segment Information - Segment Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-11-business-segment-information-segment-information-details</Role>
      <ShortName>Note 11 - Business Segment Information - Segment Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>053 - Disclosure - Note 12 - Commitments and Contingencies (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-12-commitments-and-contingencies-details-textual</Role>
      <ShortName>Note 12 - Commitments and Contingencies (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-12-commitments-and-contingencies-tables</ParentRole>
      <Position>54</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>054 - Disclosure - Note 12 - Commitments and Contingencies - Minimum Lease Payments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-12-commitments-and-contingencies-minimum-lease-payments-details</Role>
      <ShortName>Note 12 - Commitments and Contingencies - Minimum Lease Payments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="blgo-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>055 - Disclosure - Note 13 - Subsequent Events (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://biolargo.com/20191231/role/statement-note-13-subsequent-events-details-textual</Role>
      <ShortName>Note 13 - Subsequent Events (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://biolargo.com/20191231/role/statement-note-13-subsequent-events</ParentRole>
      <Position>56</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>blgo-20191231.xml</File>
    <File>blgo-20191231.xsd</File>
    <File>blgo-20191231_cal.xml</File>
    <File>blgo-20191231_def.xml</File>
    <File>blgo-20191231_lab.xml</File>
    <File>blgo-20191231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/srt/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2019-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
