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Cover - USD ($)
 12 Months Ended
Dec. 31, 2025
Feb. 20, 2026
Jun. 30, 2025
Jun. 30, 2024
Cover [Line Items]        
Entity Registrant Name MGE Energy, Inc.      
Entity Central Index Key 0001161728      
Document Type 10-K      
Document Period End Date Dec. 31, 2025      
Amendment Flag false      
Trading Symbol MGEE      
Document Fiscal Year Focus 2025      
Document Fiscal Period Focus FY      
Current Fiscal Year End Date --12-31      
Entity Well-known Seasoned Issuer Yes      
Entity Voluntary Filers No      
Entity Current Reporting Status Yes      
Entity Filer Category Large Accelerated Filer      
Entity Public Float     $ 3,223,355,207  
Entity Common Stock, Shares Outstanding   36,563,899    
Entity Emerging Growth Company false      
Document Financial Statement Error Correction [Flag] false      
Entity Small Business false      
ICFR Auditor Attestation Flag true      
Entity Shell Company false      
Entity Interactive Data Current Yes      
Security Exchange Name NASDAQ      
Security 12(b) Title Common Stock, $1 Par Value Per Share      
Entity Tax Identification Number 39-2040501      
Securities Act File Number 000-49965      
Entity Incorporation, State or Country Code WI      
Entity Address, Address Line One 133 South Blair Street      
Entity Address, City or Town Madison      
Entity Address, State or Province WI      
Entity Address, Postal Zip Code 53788      
City Area Code 608      
Local Phone Number 252-7000      
Document Transition Report false      
Document Annual Report true      
Documents Incorporated By Reference

DOCUMENTS INCORPORATED BY REFERENCE

 

Portions of MGE Energy, Inc.'s definitive proxy statement to be filed before April 30, 2026, relating to its annual meeting of shareholders, are incorporated by reference into Part III of this annual report on Form 10-K.

      
MGE [Member]        
Cover [Line Items]        
Entity Registrant Name Madison Gas and Electric Company      
Entity Central Index Key 0000061339      
Entity Well-known Seasoned Issuer Yes      
Entity Voluntary Filers No      
Entity Current Reporting Status Yes      
Entity Filer Category Non-accelerated Filer      
Entity Public Float       $ 0
Entity Common Stock, Shares Outstanding   17,347,894    
Entity Emerging Growth Company false      
Entity Small Business false      
Entity Shell Company false      
Entity Interactive Data Current Yes      
Entity Tax Identification Number 39-0444025      
Securities Act File Number 000-1125      
Entity Incorporation, State or Country Code WI      
Entity Address, Address Line One 133 South Blair Street      
Entity Address, City or Town Madison      
Entity Address, State or Province WI      
Entity Address, Postal Zip Code 53788      
City Area Code 608      
Local Phone Number 252-7000      
Document Transition Report false      
Document Annual Report true