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Schedule I - Condensed Parent Company Finanical Statements (Details-Notes 1) - Line of Credit [Member] - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Credit facilities [Line Items]    
Available lines of credit [1] $ 150,000 $ 150,000
MGE Energy unsecured committed revolving line of credit totaling $50 million | MGE Energy [Member]    
Credit facilities [Line Items]    
Available lines of credit 50,000  
Line of credit, borrowings outstanding $ 0  
[1]

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