v3.26.3
Summary of Significant Accounting Principles (Details-1) - USD ($)
$ in Thousands
9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Dec. 31, 2024
Supplemental Cash Flow Information [Abstract]        
US Federal [1] $ (8,353) $ 5,431    
Accrued capital expenditures 19,040 14,785    
Short-Term Debt [Abstract]        
Short-Term Debt 50,250   $ 94,527  
Cash, Cash Equivalents, And Restricted Cash [Abstract]        
Cash and cash equivalents 10,539   5,666  
Restricted cash 731   952  
Receivable - margin account 2,623   2,118  
Cash, cash equivalents, and restricted cash 13,893 14,020 8,736 $ 24,496
Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]        
Effects of The Inflation Reduction Act [Abstract]        
Guarantor Obligations, Liquidation Proceeds, Monetary Amount 12,200      
Wisconsin        
Supplemental Cash Flow Information [Abstract]        
US State and Local 6,000 7,000    
US State and Local - Other        
Supplemental Cash Flow Information [Abstract]        
US State and Local 91 66    
MGE [Member]        
Supplemental Cash Flow Information [Abstract]        
US Federal [1],[2] (9,623) 4,211    
Accrued capital expenditures [2] 19,040 14,785    
Short-Term Debt [Abstract]        
Short-Term Debt 50,250   94,527  
Cash, Cash Equivalents, And Restricted Cash [Abstract]        
Cash and cash equivalents 2,638   2,248  
Restricted cash 731   952  
Receivable - margin account 2,623   2,118  
Cash, cash equivalents, and restricted cash 5,992 7,128 $ 5,318 $ 20,059
MGE [Member] | Wisconsin        
Supplemental Cash Flow Information [Abstract]        
US State and Local [2] 5,650 6,540    
MGE [Member] | US State and Local - Other        
Supplemental Cash Flow Information [Abstract]        
US State and Local [2] $ 0 $ 0    
[1] For the nine months ended September 30, 2026, federal tax receipts include $12.2 million of proceeds from the transfer of federal tax credits under Internal Revenue Code Section 6418.
[2] MGE Energy files a consolidated federal income tax return with its subsidiaries. While taxes are filed on a consolidated basis, MGE calculates its respective share of tax liability and makes intercompany tax payments to or from its parent company.