<?xml version="1.0" encoding="utf-8"?>
<FilingSummary xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Version>2.3.0.15</Version>
  <ProcessingTime />
  <ReportFormat>Html</ReportFormat>
  <ReportType />
  <ContextCount>246</ContextCount>
  <ElementCount>305</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>47</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>8</UnitCount>
  <MyReports>
    <Report>
      <IsDefault>true</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>010010 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>010020 - Statement - MGE Energy Inc Consolidated Statements of Income (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/MGEEnergyIncConsolidatedStatementsOfIncomeUnaudited</Role>
      <ShortName>MGE Energy Inc Consolidated Statements of Income (Unaudited)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>010025 - Statement - Madison Gas and Electric Company Consolidated Statements of Income (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/StatementMadisonGasAndElectricCompanyConsolidatedStatementsOfIncomeUnaudited</Role>
      <ShortName>Madison Gas and Electric Company Consolidated Statements of Income (Unaudited)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>010030 - Statement - Consolidated Balance Sheets (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/StatementConsolidatedBalanceSheetsUnaudited</Role>
      <ShortName>Consolidated Balance Sheets (Unaudited)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>010040 - Statement - Consolidated Balance Sheets (Unaudited) (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/StatementConsolidatedBalanceSheetsUnauditedParentheticals</Role>
      <ShortName>Consolidated Balance Sheets (Unaudited) (Parentheticals)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>010050 - Statement - MGE Energy Inc Consolidated Statements of Cash Flows (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/StatementMGEEnergyIncConsolidatedStatementsOfCashFlowsUnaudited</Role>
      <ShortName>MGE Energy Inc Consolidated Statements of Cash Flows (Unaudited)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>010055 - Statement - Madison Gas and Electric Company Consolidated Statements of Cash Flows (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/StatementMadisonGasAndElectricCompanyConsolidatedStatementsOfCashFlowsUnaudited</Role>
      <ShortName>Madison Gas and Electric Company Consolidated Statements of Cash Flows (Unaudited)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>010060 - Statement - MGE Energy Inc Consolidated Statements of Common Equity (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/MGEEnergyIncConsolidatedStatementsOfCommonEquityUnaudited</Role>
      <ShortName>MGE Energy Inc Consolidated Statements of Common Equity (Unaudited)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>010065 - Statement - Madison Gas and Electric Company Consolidated Statements of Common Equity (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/MadisonGasAndElectricCompanyConsolidatedStatementsOfCommonEquityUnaudited</Role>
      <ShortName>Madison Gas and Electric Company Consolidated Statements of Common Equity (Unaudited)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>010070 - Statement - Consolidated Statements of Common Equity (Unaudited) (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/ConsolidatedStatementsOfCommonEquityUnauditedParentheticals</Role>
      <ShortName>Consolidated Statements of Common Equity (Unaudited) (Parentheticals)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>010090 - Disclosure - Basis of Presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureBasisOfPresentation</Role>
      <ShortName>Basis of Presentation</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>010100 - Disclosure - Equity and Financing Arrangements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureEquityAndFinancingArrangements</Role>
      <ShortName>Equity and Financing Arrangements</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>010110 - Disclosure - Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureComprehensiveIncome</Role>
      <ShortName>Comprehensive Income</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>010120 - Disclosure - Investment in ATC</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureInvestmentInATC</Role>
      <ShortName>Investment in ATC</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>010130 - Disclosure - Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureTaxes</Role>
      <ShortName>Taxes</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>010140 - Disclosure - Elm Road</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureElmRoad</Role>
      <ShortName>Elm Road</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>010210 - Disclosure - Pension and Other Postretirement Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosurePensionAndOtherPostretirementPlans</Role>
      <ShortName>Pension and Other Postretirement Plans</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>010220 - Disclosure - Share-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/ShareBasedCompensation</Role>
      <ShortName>Share-Based Compensation</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>010225 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>010230 - Disclosure - Blount Station</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureBlountStation</Role>
      <ShortName>Blount Station</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>010240 - Disclosure - Derivative and Hedging Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureDerivativeAndHedgingInstruments</Role>
      <ShortName>Derivative and Hedging Instruments</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>010270 - Disclosure - Rate Matters</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureRateMatters</Role>
      <ShortName>Rate Matters</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>010280 - Disclosure - Fair Value of Financial Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureFairValueOfFinancialInstruments</Role>
      <ShortName>Fair Value of Financial Instruments</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>010290 - Disclosure - New Accounting Pronouncements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureNewAccountingPronouncements</Role>
      <ShortName>New Accounting Pronouncements</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>010310 - Disclosure - Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureSegmentInformation</Role>
      <ShortName>Segment Information</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>010340 - Disclosure - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureSubsequentEvents</Role>
      <ShortName>Subsequent Events</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>020000 - Disclosure - Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Significant Accounting Policies (Policies)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>030000 - Disclosure - Comprehensive Income (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureComprehensiveIncomeTables</Role>
      <ShortName>Comprehensive Income (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>030010 - Disclosure - Investment in ATC (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureInvestmentInATCTables</Role>
      <ShortName>Investment in ATC (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>030020 - Disclosure - Pension and Other Postretirement Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosurePensionAndOtherPostretirementPlansTables</Role>
      <ShortName>Pension and Other Postretirement Plans (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>030030 - Disclosure - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureCommitmentsAndContingenciesTables</Role>
      <ShortName>Commitments and Contingencies (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>030040 - Disclosure - Blount Station (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureBlountStationTables</Role>
      <ShortName>Blount Station (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>030050 - Disclosure - Derivative and Hedging Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureDerivativeAndHedgingInstrumentsTables</Role>
      <ShortName>Derivative and Hedging Instruments (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>030060 - Disclosure - Fair Value of Financial Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureFairValueOfFinancialInstrumentsTables</Role>
      <ShortName>Fair Value of Financial Instruments (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>030070 - Disclosure - Segment Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureSegmentInformationTables</Role>
      <ShortName>Segment Information (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>040000 - Disclosure - Equity and Financing Arrangements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureEquityAndFinancingArrangementsDetails</Role>
      <ShortName>Equity and Financing Arrangements (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>040010 - Disclosure - MGE Energy Inc Comprehensive Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/MGEEnergyIncComprehensiveIncomeDetails</Role>
      <ShortName>MGE Energy Inc Comprehensive Income (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>040015 - Disclosure - Madison Gas and Electric Company Comprehensive Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/MadisonGasAndElectricCompanyComprehensiveIncomeDetails</Role>
      <ShortName>Madison Gas and Electric Company Comprehensive Income (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>040020 - Disclosure - Investment in ATC (Details-1)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureInvestmentInATCDetails1</Role>
      <ShortName>Investment in ATC (Details-1)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>040025 - Disclosure - Investment in ATC (Details-2)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureInvestmentInATCDetails2</Role>
      <ShortName>Investment in ATC (Details-2)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>040030 - Disclosure - Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureTaxesDetails</Role>
      <ShortName>Taxes (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>040040 - Disclosure - Elm Road (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureElmRoadDetails</Role>
      <ShortName>Elm Road (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>040050 - Disclosure - Pension and Other Postretirement Plans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosurePensionAndOtherPostretirementPlansDetails</Role>
      <ShortName>Pension and Other Postretirement Plans (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>040060 - Disclosure - Share Based Compensation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureShareBasedCompensationDetails</Role>
      <ShortName>Share Based Compensation (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>040070 - Disclosure - Commitments and Contingencies (Details-1)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureCommitmentsAndContingenciesDetails1</Role>
      <ShortName>Commitments and Contingencies (Details-1)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>040075 - Disclosure - Commitments and Contingencies (Details-2)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureCommitmentsAndContingenciesDetails2</Role>
      <ShortName>Commitments and Contingencies (Details-2)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>040080 - Disclosure - Blount Station (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureBlountStationDetails</Role>
      <ShortName>Blount Station (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>040090 - Disclosure - Derivative and Hedging Instruments (Details-1)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureDerivativeAndHedgingInstrumentsDetails1</Role>
      <ShortName>Derivative and Hedging Instruments (Details-1)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>040091 - Disclosure - Derivative and Hedging Instruments (Details-2)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureDerivativeAndHedgingInstrumentsDetails2</Role>
      <ShortName>Derivative and Hedging Instruments (Details-2)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>040092 - Disclosure - Derivative and Hedging Instruments (Details-3)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureDerivativeAndHedgingInstrumentsDetails3</Role>
      <ShortName>Derivative and Hedging Instruments (Details-3)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>040110 - Disclosure - Rate Matters (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureRateMattersDetails</Role>
      <ShortName>Rate Matters (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>040120 - Disclosure - Fair Value of Financial Instruments (Details-1)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureFairValueOfFinancialInstrumentsDetails1</Role>
      <ShortName>Fair Value of Financial Instruments (Details-1)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>040121 - Disclosure - Fair Value of Financial Instruments (Details-2)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureFairValueOfFinancialInstrumentsDetails2</Role>
      <ShortName>Fair Value of Financial Instruments (Details-2)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>040122 - Disclosure - Fair Value of Financial Instruments (Details-3)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureFairValueOfFinancialInstrumentsDetails3</Role>
      <ShortName>Fair Value of Financial Instruments (Details-3)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>040130 - Disclosure - Segment Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureSegmentInformationDetails</Role>
      <ShortName>Segment Information (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>040140 - Disclosure - Subsequent Events (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.mgeenergy.com/role/DisclosureSubsequentEventsDetails</Role>
      <ShortName>Subsequent Events (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <Logs>
    <Log type="Info">'Monetary' elements on report '040020 - Disclosure - Investment in ATC (Details-1)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '040050 - Disclosure - Pension and Other Postretirement Plans (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '040070 - Disclosure - Commitments and Contingencies (Details-1)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '040075 - Disclosure - Commitments and Contingencies (Details-2)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '040080 - Disclosure - Blount Station (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '040090 - Disclosure - Derivative and Hedging Instruments (Details-1)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '040092 - Disclosure - Derivative and Hedging Instruments (Details-3)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '040121 - Disclosure - Fair Value of Financial Instruments (Details-2)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">Process Flow-Through: 010020 - Statement - MGE Energy Inc Consolidated Statements of Income (Unaudited)</Log>
    <Log type="Info">Process Flow-Through: 010025 - Statement - Madison Gas and Electric Company Consolidated Statements of Income (Unaudited)</Log>
    <Log type="Info">Process Flow-Through: 010030 - Statement - Consolidated Balance Sheets (Unaudited)</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Sep. 30, 2010'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2009'</Log>
    <Log type="Info">Process Flow-Through: 010040 - Statement - Consolidated Balance Sheets (Unaudited) (Parentheticals)</Log>
    <Log type="Info">Process Flow-Through: 010050 - Statement - MGE Energy Inc Consolidated Statements of Cash Flows (Unaudited)</Log>
    <Log type="Info">Process Flow-Through: 010055 - Statement - Madison Gas and Electric Company Consolidated Statements of Cash Flows (Unaudited)</Log>
    <Log type="Info">Process Flow-Through: 010070 - Statement - Consolidated Statements of Common Equity (Unaudited) (Parentheticals)</Log>
  </Logs>
  <InputFiles>
    <File>mgee-20110930.xml</File>
    <File>mgee-20110930.xsd</File>
    <File>mgee-20110930_cal.xml</File>
    <File>mgee-20110930_def.xml</File>
    <File>mgee-20110930_lab.xml</File>
    <File>mgee-20110930_pre.xml</File>
  </InputFiles>
  <SupplementalFiles />
  <BaseTaxonomies />
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
