Document and Entity Information
Apr. 16, 2021
Document And Entity Information [Line Items]  
Entity Registrant Name MGE Energy, Inc.
Entity Central Index Key 0001161728
Document Type 8-K
Document Period End Date Apr. 16, 2021
Amendment Flag false
Trading Symbol MGEE
Entity Emerging Growth Company false
Security Exchange Name NASDAQ
Security 12b Title Common Stock, $1 Par Value Per Share
Entity Tax Identification Number 39-2040501
Entity File Number 000-49965
Entity Address Address Line1 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
Written Communications false
Soliciting Material false
Pre-commencement Issuer Tender Offer false
Pre-commencement Tender Offer false
Entity Incorporation State Country Code WI
MGE [Member]  
Document And Entity Information [Line Items]  
Entity Registrant Name Madison Gas and Electric Company
Entity Central Index Key 0000061339
Entity Emerging Growth Company false
Entity Tax Identification Number 39-0444025
Entity File Number 000-1125
Entity Address Address Line1 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
Entity Incorporation State Country Code WI