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Notes Payable to Banks, Commercial Paper, and Lines of Credit (Details)
$ in Thousands
12 Months Ended
Dec. 31, 2021
USD ($)
Dec. 31, 2020
USD ($)
Short-term Debt [Line Items]    
Short-term debt outstanding [1] $ 5,500 $ 52,500
Letters of credit issued inside credit facilities [1] $ 685 $ 685
Weighted-average interest rate [1] 0.15% 0.15%
Maximum short-term borrowings [1] $ 64,000 $ 52,500
Average short-term borrowings [1] $ 28,583 $ 6,393
Weighted-average interest rate during the year [1] 0.15% 0.43%
Line of Credit [Member]    
Short-term Debt [Line Items]    
Available capacity under line of credit [1] $ 143,815 $ 96,815
Line of Credit [Member] | MGE Energy unsecured committed revolving line of credit totaling $50 million [Member] | MGE Energy [Member]    
Short-term Debt [Line Items]    
Line of credit 50,000  
Line of credit, borrowings outstanding $ 0  
Debt covenant, required parent company ownership of MGE 100.00%  
Line of Credit [Member] | MGE Energy unsecured committed revolving line of credit totaling $50 million [Member] | Minimum [Member] | MGE Energy [Member]    
Short-term Debt [Line Items]    
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value 30.00%  
Line of Credit [Member] | MGE Energy unsecured committed revolving line of credit totaling $50 million [Member] | Maximum [Member] | MGE Energy [Member]    
Short-term Debt [Line Items]    
Debt to total capitalization ratio 0.65  
MGE [Member]    
Short-term Debt [Line Items]    
Short-term debt outstanding $ 5,500 52,500
Letters of credit issued inside credit facilities $ 685 $ 685
Weighted-average interest rate 0.15% 0.15%
Maximum short-term borrowings $ 64,000 $ 52,500
Average short-term borrowings $ 28,583 $ 6,393
Weighted-average interest rate during the year 0.15% 0.43%
MGE [Member] | Line of Credit [Member]    
Short-term Debt [Line Items]    
Available capacity under line of credit $ 93,815 $ 46,815
MGE [Member] | Line of Credit [Member] | MGE unsecured committed revolving lines of credit totaling $100 million [Member]    
Short-term Debt [Line Items]    
Line of credit 100,000  
Line of credit, borrowings outstanding $ 0  
Debt covenant, required parent company ownership of MGE 100.00%  
MGE [Member] | Line of Credit [Member] | MGE unsecured committed revolving lines of credit totaling $100 million [Member] | Minimum [Member]    
Short-term Debt [Line Items]    
Debt covenant, ownership interest by outside party resulting in repurchase of notes at par value 30.00%  
MGE [Member] | Line of Credit [Member] | MGE unsecured committed revolving lines of credit totaling $100 million [Member] | Maximum [Member]    
Short-term Debt [Line Items]    
Debt to total capitalization ratio 0.65  
[1] MGE Energy short-term borrowings include MGE Energy and MGE lines of credit and MGE commercial paper.