<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.22.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>258</ContextCount>
  <ElementCount>345</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>75</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>10</UnitCount>
  <MyReports>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001001 - Document - Cover Page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/CoverPage</Role>
      <ShortName>Cover Page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001002 - Statement - Condensed Consolidated Balance Sheets (unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/CondensedConsolidatedBalanceSheetsunaudited</Role>
      <ShortName>Condensed Consolidated Balance Sheets (unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1002003 - Statement - Condensed Consolidated Balance Sheets (unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/CondensedConsolidatedBalanceSheetsunauditedParenthetical</Role>
      <ShortName>Condensed Consolidated Balance Sheets (unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1003004 - Statement - Condensed Consolidated Statements of Operations (unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/CondensedConsolidatedStatementsofOperationsunaudited</Role>
      <ShortName>Condensed Consolidated Statements of Operations (unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1004005 - Statement - Condensed Consolidated Statements of Comprehensive Income (Loss) (unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/CondensedConsolidatedStatementsofComprehensiveIncomeLossunaudited</Role>
      <ShortName>Condensed Consolidated Statements of Comprehensive Income (Loss) (unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1005006 - Statement - Condensed Consolidated Statements of Comprehensive Income (Loss) (unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/CondensedConsolidatedStatementsofComprehensiveIncomeLossunauditedParenthetical</Role>
      <ShortName>Condensed Consolidated Statements of Comprehensive Income (Loss) (unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1006007 - Statement - Condensed Consolidated Statements of Equity (unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/CondensedConsolidatedStatementsofEquityunaudited</Role>
      <ShortName>Condensed Consolidated Statements of Equity (unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>1007008 - Statement - Condensed Consolidated Statements of Equity (unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/CondensedConsolidatedStatementsofEquityunauditedParenthetical</Role>
      <ShortName>Condensed Consolidated Statements of Equity (unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>1008009 - Statement - Condensed Consolidated Statements of Cash Flows (unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/CondensedConsolidatedStatementsofCashFlowsunaudited</Role>
      <ShortName>Condensed Consolidated Statements of Cash Flows (unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2101101 - Disclosure - Basis of Presentation and Nature of the Business</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/BasisofPresentationandNatureoftheBusiness</Role>
      <ShortName>Basis of Presentation and Nature of the Business</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2103102 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/SummaryofSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2111103 - Disclosure - Acquisitions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/Acquisitions</Role>
      <ShortName>Acquisitions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2115104 - Disclosure - Marketable Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/MarketableSecurities</Role>
      <ShortName>Marketable Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2118105 - Disclosure - Inventories</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/Inventories</Role>
      <ShortName>Inventories</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2122106 - Disclosure - Other Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/OtherAssets</Role>
      <ShortName>Other Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2127107 - Disclosure - Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/IntangibleAssets</Role>
      <ShortName>Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2132108 - Disclosure - Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/Debt</Role>
      <ShortName>Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2137109 - Disclosure - Derivative Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/DerivativeInstruments</Role>
      <ShortName>Derivative Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2142110 - Disclosure - Fair Value Measurement</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/FairValueMeasurement</Role>
      <ShortName>Fair Value Measurement</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2146111 - Disclosure - Net Income Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/NetIncomePerShare</Role>
      <ShortName>Net Income Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2149112 - Disclosure - Reportable Segments and Geographic Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/ReportableSegmentsandGeographicInformation</Role>
      <ShortName>Reportable Segments and Geographic Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2153113 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/CommitmentsandContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2157114 - Disclosure - Proposed Plan of Merger</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/ProposedPlanofMerger</Role>
      <ShortName>Proposed Plan of Merger</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2159115 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/SubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2204201 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/SummaryofSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/SummaryofSignificantAccountingPolicies</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2305301 - Disclosure - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/SummaryofSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/SummaryofSignificantAccountingPolicies</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2312302 - Disclosure - Acquisitions (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/AcquisitionsTables</Role>
      <ShortName>Acquisitions (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/Acquisitions</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2316303 - Disclosure - Marketable Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/MarketableSecuritiesTables</Role>
      <ShortName>Marketable Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/MarketableSecurities</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2319304 - Disclosure - Inventories (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/InventoriesTables</Role>
      <ShortName>Inventories (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/Inventories</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2323305 - Disclosure - Other Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/OtherAssetsTables</Role>
      <ShortName>Other Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/OtherAssets</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2328306 - Disclosure - Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/IntangibleAssetsTables</Role>
      <ShortName>Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/IntangibleAssets</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2333307 - Disclosure - Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/DebtTables</Role>
      <ShortName>Debt (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/Debt</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2338308 - Disclosure - Derivative Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/DerivativeInstrumentsTables</Role>
      <ShortName>Derivative Instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/DerivativeInstruments</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2343309 - Disclosure - Fair Value Measurement (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/FairValueMeasurementTables</Role>
      <ShortName>Fair Value Measurement (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/FairValueMeasurement</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2347310 - Disclosure - Net Income Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/NetIncomePerShareTables</Role>
      <ShortName>Net Income Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/NetIncomePerShare</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2350311 - Disclosure - Reportable Segments and Geographic Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/ReportableSegmentsandGeographicInformationTables</Role>
      <ShortName>Reportable Segments and Geographic Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/ReportableSegmentsandGeographicInformation</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2354312 - Disclosure - Commitment and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/CommitmentandContingenciesTables</Role>
      <ShortName>Commitment and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2402401 - Disclosure - Basis of Presentation and Nature of the Business (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/BasisofPresentationandNatureoftheBusinessDetails</Role>
      <ShortName>Basis of Presentation and Nature of the Business (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/BasisofPresentationandNatureoftheBusiness</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2406402 - Disclosure - Summary of Significant Accounting Policies - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2407403 - Disclosure - Summary of Significant Accounting Policies - Restricted Cash (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/SummaryofSignificantAccountingPoliciesRestrictedCashDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Restricted Cash (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2408404 - Disclosure - Summary of Significant Accounting Policies - Disaggregation of Revenue (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/SummaryofSignificantAccountingPoliciesDisaggregationofRevenueDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Disaggregation of Revenue (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2409405 - Disclosure - Summary of Significant Accounting Policies - Contract Balances (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/SummaryofSignificantAccountingPoliciesContractBalancesDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Contract Balances (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2410406 - Disclosure - Summary of Significant Accounting Policies - Significant Changes in Contract Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/SummaryofSignificantAccountingPoliciesSignificantChangesinContractLiabilitiesDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Significant Changes in Contract Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2413407 - Disclosure - Acquisitions - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/AcquisitionsNarrativeDetails</Role>
      <ShortName>Acquisitions - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2414408 - Disclosure - Acquisitions - Assets Acquired and Liabilities Assumed (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/AcquisitionsAssetsAcquiredandLiabilitiesAssumedDetails</Role>
      <ShortName>Acquisitions - Assets Acquired and Liabilities Assumed (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2417409 - Disclosure - Marketable Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/MarketableSecuritiesDetails</Role>
      <ShortName>Marketable Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/MarketableSecuritiesTables</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2420410 - Disclosure - Inventories - Components (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/InventoriesComponentsDetails</Role>
      <ShortName>Inventories - Components (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2421411 - Disclosure - Inventories - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/InventoriesNarrativeDetails</Role>
      <ShortName>Inventories - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2424412 - Disclosure - Other Assets - Prepaid Expenses and Other Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/OtherAssetsPrepaidExpensesandOtherAssetsDetails</Role>
      <ShortName>Other Assets - Prepaid Expenses and Other Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2425413 - Disclosure - Other Assets - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/OtherAssetsNarrativeDetails</Role>
      <ShortName>Other Assets - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2426414 - Disclosure - Other Assets - Other Noncurrent Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/OtherAssetsOtherNoncurrentAssetsDetails</Role>
      <ShortName>Other Assets - Other Noncurrent Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2429415 - Disclosure - Intangible Assets - Components (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/IntangibleAssetsComponentsDetails</Role>
      <ShortName>Intangible Assets - Components (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2430416 - Disclosure - Intangible Assets - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/IntangibleAssetsNarrativeDetails</Role>
      <ShortName>Intangible Assets - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2431417 - Disclosure - Intangible Assets - Estimated Amortization Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/IntangibleAssetsEstimatedAmortizationExpenseDetails</Role>
      <ShortName>Intangible Assets - Estimated Amortization Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2434418 - Disclosure - Debt - Components (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/DebtComponentsDetails</Role>
      <ShortName>Debt - Components (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2435419 - Disclosure - Debt - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/DebtNarrativeDetails</Role>
      <ShortName>Debt - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2436420 - Disclosure - Debt - Line of Credit (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/DebtLineofCreditDetails</Role>
      <ShortName>Debt - Line of Credit (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>2439421 - Disclosure - Derivative Instruments - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/DerivativeInstrumentsNarrativeDetails</Role>
      <ShortName>Derivative Instruments - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>2440422 - Disclosure - Derivative Instruments - Derivative Financial Instruments by Balance Sheet Location (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/DerivativeInstrumentsDerivativeFinancialInstrumentsbyBalanceSheetLocationDetails</Role>
      <ShortName>Derivative Instruments - Derivative Financial Instruments by Balance Sheet Location (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>2441423 - Disclosure - Derivative Instruments - Gains (Losses) included in the Statements of Operations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/DerivativeInstrumentsGainsLossesincludedintheStatementsofOperationsDetails</Role>
      <ShortName>Derivative Instruments - Gains (Losses) included in the Statements of Operations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>2444424 - Disclosure - Fair Value Measurement - Summary of Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/FairValueMeasurementSummaryofAssetsandLiabilitiesDetails</Role>
      <ShortName>Fair Value Measurement - Summary of Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>2445425 - Disclosure - Fair Value Measurement - Estimated Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/FairValueMeasurementEstimatedFairValueDetails</Role>
      <ShortName>Fair Value Measurement - Estimated Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>2448426 - Disclosure - Net Income Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/NetIncomePerShareDetails</Role>
      <ShortName>Net Income Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/NetIncomePerShareTables</ParentRole>
      <Position>63</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>2451427 - Disclosure - Reportable Segments and Geographic Information - Significant Items by Reportable Segment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/ReportableSegmentsandGeographicInformationSignificantItemsbyReportableSegmentDetails</Role>
      <ShortName>Reportable Segments and Geographic Information - Significant Items by Reportable Segment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>2452428 - Disclosure - Reportable Segments and Geographic Information - Geographic Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/ReportableSegmentsandGeographicInformationGeographicInformationDetails</Role>
      <ShortName>Reportable Segments and Geographic Information - Geographic Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>2455429 - Disclosure - Commitments and Contingencies - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/CommitmentsandContingenciesNarrativeDetails</Role>
      <ShortName>Commitments and Contingencies - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>2456430 - Disclosure - Commitments and Contingencies - Schedule of Minimum Contract Commitments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/CommitmentsandContingenciesScheduleofMinimumContractCommitmentsDetails</Role>
      <ShortName>Commitments and Contingencies - Schedule of Minimum Contract Commitments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>2458431 - Disclosure - Proposed Plan of Merger (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/ProposedPlanofMergerDetails</Role>
      <ShortName>Proposed Plan of Merger (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/ProposedPlanofMerger</ParentRole>
      <Position>68</Position>
    </Report>
    <Report instance="regi-20220331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>2460432 - Disclosure - Subsequent Events (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.regfuel.com/role/SubsequentEventsDetails</Role>
      <ShortName>Subsequent Events (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.regfuel.com/role/SubsequentEvents</ParentRole>
      <Position>69</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="regi-20220331.htm">regi-20220331.htm</File>
    <File>regi-20220331.xsd</File>
    <File>regi-20220331_cal.xml</File>
    <File>regi-20220331_def.xml</File>
    <File>regi-20220331_lab.xml</File>
    <File>regi-20220331_pre.xml</File>
    <File>regi2022q1ex311.htm</File>
    <File>regi2022q1ex312.htm</File>
    <File>regi2022q1ex321.htm</File>
    <File>regi2022q1ex322.htm</File>
  </InputFiles>
  <SupplementalFiles>
    <File>regi-20220331_g1.jpg</File>
    <File>regi-20220331_g2.jpg</File>
    <File>regi-20220331_g3.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="1">http://fasb.org/srt/2021-01-31</BaseTaxonomy>
    <BaseTaxonomy items="756">http://fasb.org/us-gaap/2021-01-31</BaseTaxonomy>
    <BaseTaxonomy items="29">http://xbrl.sec.gov/dei/2021q4</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
