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Schedule I - Condensed Parent Company Finanical Statements (Details-Notes 1) (Line of Credit [Member], USD $)
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Credit facilities [Line Items]      
Available lines of credit $ 150,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity [1] $ 150,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity [1] $ 115,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity [1]
MGE Energy [Member] | MGE Energy $50 million unsecured commiteed revolving line of credit      
Credit facilities [Line Items]      
Available lines of credit 50,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
/ us-gaap_DebtInstrumentAxis
= mgee_MgeEnergyFiftyMillionUnsecuredCommittedRevolvingLineOfCreditMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_LineOfCreditMember
   
Line of credit, borrowings outstanding $ 0us-gaap_LineOfCredit
/ us-gaap_DebtInstrumentAxis
= mgee_MgeEnergyFiftyMillionUnsecuredCommittedRevolvingLineOfCreditMember
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_ShortTermDebtTypeAxis
= us-gaap_LineOfCreditMember
   
[1]

MGE Energy short-term borrowings include MGE Energy and MGE lines of credit and MGE commercial paper.