Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2016	Oct. 31, 2016
Document And Entity Information [Line Items]
Entity Registrant Name	MGE Energy Inc
Entity Central Index Key	0001161728
Document Type	10-Q
Document Period End Date	Sep. 30, 2016
Amendment Flag	false
Trading Symbol	MGEE
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	Q3
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 Common Stock Shares Outstanding		34,668,370
MGE [Member]
Document And Entity Information [Line Items]
Entity Registrant Name	Madison Gas and Electric Company
Entity Central Index Key	0000061339
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Common Stock Shares Outstanding		17,347,894