<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.23.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>249</ContextCount>
  <ElementCount>250</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>70</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>7</UnitCount>
  <MyReports>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>100000 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>100010 - Statement - INTERIM CONSOLIDATED STATEMENTS OF OPERATIONS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_StatementINTERIMCONSOLIDATEDSTATEMENTSOFOPERATIONS</Role>
      <ShortName>INTERIM CONSOLIDATED STATEMENTS OF OPERATIONS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>100020 - Statement - INTERIM CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_StatementINTERIMCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMELOSS</Role>
      <ShortName>INTERIM CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>100030 - Statement - INTERIM CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_StatementINTERIMCONSOLIDATEDBALANCESHEETS</Role>
      <ShortName>INTERIM CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>100040 - Statement - INTERIM CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_StatementINTERIMCONSOLIDATEDBALANCESHEETSParenthetical</Role>
      <ShortName>INTERIM CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>100050 - Statement - INTERIM CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_StatementINTERIMCONSOLIDATEDSTATEMENTSOFCHANGESINSHAREHOLDERSEQUITY</Role>
      <ShortName>INTERIM CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>100060 - Statement - INTERIM CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_StatementINTERIMCONSOLIDATEDSTATEMENTSOFCASHFLOWS</Role>
      <ShortName>INTERIM CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>100070 - Disclosure - The Company and Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureTheCompanyAndSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>The Company and Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>100080 - Disclosure - Torgau Acquisition</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/DisclosureTorgauAcquisition</Role>
      <ShortName>Torgau Acquisition</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>100090 - Disclosure - Business Interruption Insurance</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureBusinessInterruptionInsurance</Role>
      <ShortName>Business Interruption Insurance</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>100100 - Disclosure - Inventories</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureInventories</Role>
      <ShortName>Inventories</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>100110 - Disclosure - Accounts Payable and Other</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureAccountsPayableAndOther</Role>
      <ShortName>Accounts Payable and Other</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>100120 - Disclosure - Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureDebt</Role>
      <ShortName>Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>100130 - Disclosure - Pension and Other Post-Retirement Benefit Obligations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosurePensionAndOtherPostRetirementBenefitObligations</Role>
      <ShortName>Pension and Other Post-Retirement Benefit Obligations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>100140 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureIncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>100150 - Disclosure - Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureShareholdersEquity</Role>
      <ShortName>Shareholders' Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>100160 - Disclosure - Net Income (Loss) Per Common Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/DisclosureNetIncomeLossPerCommonShare1</Role>
      <ShortName>Net Income (Loss) Per Common Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>100170 - Disclosure - Accumulated Other Comprehensive Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureAccumulatedOtherComprehensiveLoss</Role>
      <ShortName>Accumulated Other Comprehensive Loss</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>100180 - Disclosure - Related Party Transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureRelatedPartyTransactions</Role>
      <ShortName>Related Party Transactions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>100190 - Disclosure - Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureSegmentInformation</Role>
      <ShortName>Segment Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>100200 - Disclosure - Financial Instruments and Fair Value Measurement</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureFinancialInstrumentsAndFairValueMeasurement</Role>
      <ShortName>Financial Instruments and Fair Value Measurement</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>100210 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>100220 - Disclosure - Subsequent Event</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/DisclosureSubsequentEvent</Role>
      <ShortName>Subsequent Event</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>100230 - Disclosure - The Company and Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureTheCompanyAndSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>The Company and Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureTheCompanyAndSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>100240 - Disclosure - Torgau Acquisition (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/DisclosureTorgauAcquisitionTables</Role>
      <ShortName>Torgau Acquisition (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/DisclosureTorgauAcquisition</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>100250 - Disclosure - Inventories (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureInventoriesTables</Role>
      <ShortName>Inventories (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureInventories</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>100260 - Disclosure - Accounts Payable and Other (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureAccountsPayableAndOtherTables</Role>
      <ShortName>Accounts Payable and Other (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureAccountsPayableAndOther</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>100270 - Disclosure - Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureDebtTables</Role>
      <ShortName>Debt (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureDebt</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>100280 - Disclosure - Pension and Other Post-Retirement Benefit Obligations (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosurePensionAndOtherPostRetirementBenefitObligationsTables</Role>
      <ShortName>Pension and Other Post-Retirement Benefit Obligations (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosurePensionAndOtherPostRetirementBenefitObligations</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>100290 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureIncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureIncomeTaxes</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>100300 - Disclosure - Shareholders' Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureShareholdersEquityTables</Role>
      <ShortName>Shareholders' Equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureShareholdersEquity</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>100310 - Disclosure - Net Income (Loss) Per Common Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/DisclosureNetIncomeLossPerCommonShareTables</Role>
      <ShortName>Net Income (Loss) Per Common Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/DisclosureNetIncomeLossPerCommonShare1</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>100320 - Disclosure - Accumulated Other Comprehensive Loss (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureAccumulatedOtherComprehensiveLossTables</Role>
      <ShortName>Accumulated Other Comprehensive Loss (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureAccumulatedOtherComprehensiveLoss</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>100330 - Disclosure - Segment Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureSegmentInformationTables</Role>
      <ShortName>Segment Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureSegmentInformation</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>100340 - Disclosure - Financial Instruments and Fair Value Measurement (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureFinancialInstrumentsAndFairValueMeasurementTables</Role>
      <ShortName>Financial Instruments and Fair Value Measurement (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureFinancialInstrumentsAndFairValueMeasurement</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>100350 - Disclosure - The Company and Summary of Significant Accounting Policies - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureTheCompanyAndSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails</Role>
      <ShortName>The Company and Summary of Significant Accounting Policies - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>100360 - Disclosure - Torgau Acquisition - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/DisclosureTorgauAcquisitionAdditionalInformationDetails</Role>
      <ShortName>Torgau Acquisition - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>100370 - Disclosure - Torgau Acquisition - Summary of Preliminary Allocation of Purchase Price to Estimated Fair Value of Assets Acquired and Liabilities Assumed (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/DisclosureTorgauAcquisitionSummaryOfPreliminaryAllocationOfPurchasePriceToEstimatedFairValueOfAssetsAcquiredAndLiabilitiesAssumedDetails</Role>
      <ShortName>Torgau Acquisition - Summary of Preliminary Allocation of Purchase Price to Estimated Fair Value of Assets Acquired and Liabilities Assumed (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>100380 - Disclosure - Torgau Acquisition - Summary of Preliminary Allocation of Purchase Price to Estimated Fair Value of Assets Acquired and Liabilities Assumed (Parenthetical) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/DisclosureTorgauAcquisitionSummaryOfPreliminaryAllocationOfPurchasePriceToEstimatedFairValueOfAssetsAcquiredAndLiabilitiesAssumedParenthet</Role>
      <ShortName>Torgau Acquisition - Summary of Preliminary Allocation of Purchase Price to Estimated Fair Value of Assets Acquired and Liabilities Assumed (Parenthetical) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>100390 - Disclosure - Business Interruption Insurance - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureBusinessInterruptionInsuranceAdditionalInformationDetails</Role>
      <ShortName>Business Interruption Insurance - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>100400 - Disclosure - Inventories - Components of Inventories (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureInventoriesComponentsOfInventoriesDetails</Role>
      <ShortName>Inventories - Components of Inventories (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>100410 - Disclosure - Inventories - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/DisclosureInventoriesAdditionalInformationDetails</Role>
      <ShortName>Inventories - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>100420 - Disclosure - Accounts Payable and Other - Schedule of Accounts Payable and Other (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureAccountsPayableAndOtherScheduleOfAccountsPayableAndOtherDetails</Role>
      <ShortName>Accounts Payable and Other - Schedule of Accounts Payable and Other (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>100430 - Disclosure - Debt - Schedule of Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureDebtScheduleOfDebtDetails</Role>
      <ShortName>Debt - Schedule of Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>100440 - Disclosure - Debt - Schedule of Debt (Parenthetical) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureDebtScheduleOfDebtParentheticalDetails</Role>
      <ShortName>Debt - Schedule of Debt (Parenthetical) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>100450 - Disclosure - Debt - Principal Maturities of Senior Notes and Credit Arrangements (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureDebtPrincipalMaturitiesOfSeniorNotesAndCreditArrangementsDetails</Role>
      <ShortName>Debt - Principal Maturities of Senior Notes and Credit Arrangements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>100460 - Disclosure - Debt - Debt Redemption Period for Senior Notes (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureDebtDebtRedemptionPeriodForSeniorNotesDetails</Role>
      <ShortName>Debt - Debt Redemption Period for Senior Notes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>100470 - Disclosure - Pension and Other Post-Retirement Benefit Obligations - Schedule of Net Benefit Costs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosurePensionAndOtherPostRetirementBenefitObligationsScheduleOfNetBenefitCostsDetails</Role>
      <ShortName>Pension and Other Post-Retirement Benefit Obligations - Schedule of Net Benefit Costs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>100480 - Disclosure - Pension and Other Post-Retirement Benefit Obligations - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosurePensionAndOtherPostRetirementBenefitObligationsAdditionalInformationDetails</Role>
      <ShortName>Pension and Other Post-Retirement Benefit Obligations - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>100490 - Disclosure - Income Taxes - Reconciliation of Effective Tax Rate (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureIncomeTaxesReconciliationOfEffectiveTaxRateDetails</Role>
      <ShortName>Income Taxes - Reconciliation of Effective Tax Rate (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>100500 - Disclosure - Shareholders' Equity - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureShareholdersEquityAdditionalInformationDetails</Role>
      <ShortName>Shareholders' Equity - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>100510 - Disclosure - Shareholders' Equity - Summary of Share Activity - PSU's (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureShareholdersEquitySummaryOfShareActivityPSUSDetails</Role>
      <ShortName>Shareholders' Equity - Summary of Share Activity - PSU's (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>100540 - Disclosure - Net Income (Loss) Per Common Share - Reconciliation of Basic and Diluted Net Income (Loss) Per Common Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/DisclosureNetIncomeLossPerCommonShareReconciliationOfBasicAndDilutedNetIncomeLossPerCommonShareDetails</Role>
      <ShortName>Net Income (Loss) Per Common Share - Reconciliation of Basic and Diluted Net Income (Loss) Per Common Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/DisclosureNetIncomeLossPerCommonShareTables</ParentRole>
      <Position>53</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>100550 - Disclosure - Net Income (Loss) Per Common Share - Reconciliation of Basic and Diluted Net Income (Loss) Per Common Share (Parenthetical) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/DisclosureNetIncomeLossPerCommonShareReconciliationOfBasicAndDilutedNetIncomeLossPerCommonShareParentheticalDetails</Role>
      <ShortName>Net Income (Loss) Per Common Share - Reconciliation of Basic and Diluted Net Income (Loss) Per Common Share (Parenthetical) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/DisclosureNetIncomeLossPerCommonShareTables</ParentRole>
      <Position>54</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>100560 - Disclosure - Net Income (Loss) Per Common Share - Anti-Dilutive Instruments Excluded from Calculation of Net Income (Loss) Per Common Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/DisclosureNetIncomeLossPerCommonShareAntidilutiveInstrumentsExcludedFromCalculationOfNetIncomeLossPerCommonShareDetails</Role>
      <ShortName>Net Income (Loss) Per Common Share - Anti-Dilutive Instruments Excluded from Calculation of Net Income (Loss) Per Common Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/DisclosureNetIncomeLossPerCommonShareTables</ParentRole>
      <Position>55</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>100570 - Disclosure - Accumulated Other Comprehensive Loss - Schedule of Change in Accumulated Other Comprehensive Loss by Components (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureAccumulatedOtherComprehensiveLossScheduleOfChangeInAccumulatedOtherComprehensiveLossByComponentsDetails</Role>
      <ShortName>Accumulated Other Comprehensive Loss - Schedule of Change in Accumulated Other Comprehensive Loss by Components (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>100580 - Disclosure - Related Party Transactions - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureRelatedPartyTransactionsAdditionalInformationDetails</Role>
      <ShortName>Related Party Transactions - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>100590 - Disclosure - Segment Information - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureSegmentInformationAdditionalInformationDetails</Role>
      <ShortName>Segment Information - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>100600 - Disclosure - Segment Information - Schedule of Results by Segment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureSegmentInformationScheduleOfResultsBySegmentDetails</Role>
      <ShortName>Segment Information - Schedule of Results by Segment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>100610 - Disclosure - Segment Information - Schedule of Results by Segment (Parenthetical) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureSegmentInformationScheduleOfResultsBySegmentParentheticalDetails</Role>
      <ShortName>Segment Information - Schedule of Results by Segment (Parenthetical) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>100620 - Disclosure - Financial Instruments and Fair Value Measurement - Estimated Fair Values of Outstanding Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureFinancialInstrumentsAndFairValueMeasurementEstimatedFairValuesOfOutstandingDebtDetails</Role>
      <ShortName>Financial Instruments and Fair Value Measurement - Estimated Fair Values of Outstanding Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>100630 - Disclosure - Financial Instruments and Fair Value Measurement - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/Role_DisclosureFinancialInstrumentsAndFairValueMeasurementAdditionalInformationDetails</Role>
      <ShortName>Financial Instruments and Fair Value Measurement - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="merc-20230331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>100640 - Disclosure - Subsequent Event (Additional Information) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mercerint.com/20230331/taxonomy/role/DisclosureSubsequentEventAdditionalInformationDetails</Role>
      <ShortName>Subsequent Event (Additional Information) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.mercerint.com/20230331/taxonomy/role/DisclosureSubsequentEvent</ParentRole>
      <Position>63</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <Logs>
    <Log type="Warning">[dq-0542-Deprecated-Concept] Concept DueToRelatedPartiesCurrentAndNoncurrent in us-gaap/2022 used in 3 facts was deprecated in us-gaap/2023 as of 2023 and should not be used. merc-20230331.htm 3406</Log>
    <Log type="Warning">[dq-0542-Deprecated-Concept] Concept RelatedPartyTransactionDueFromToRelatedParty in us-gaap/2022 used in 1 facts was deprecated in us-gaap/2023 as of 2023 and should not be used. merc-20230331.htm 3406</Log>
  </Logs>
  <InputFiles>
    <File doctype="10-Q" original="merc-20230331.htm">merc-20230331.htm</File>
    <File>merc-20230331.xsd</File>
    <File>merc-20230331_cal.xml</File>
    <File>merc-20230331_def.xml</File>
    <File>merc-20230331_lab.xml</File>
    <File>merc-20230331_pre.xml</File>
    <File>merc-ex10_1.htm</File>
    <File>merc-ex31_1.htm</File>
    <File>merc-ex31_2.htm</File>
    <File>merc-ex32_1.htm</File>
    <File>merc-ex32_2.htm</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy items="663">http://fasb.org/us-gaap/2022</BaseTaxonomy>
    <BaseTaxonomy items="31">http://xbrl.sec.gov/dei/2022</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
