Investments (Details-2) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Equity method investments [Line Items]
Equity earnings in ATC	$ 8,615,000	$ 8,501,000	$ 8,173,000
Dividend income from ATC	6,728,000	6,667,000	6,285,000
Contributions to ATC	1,008,000	810,000	3,701,000
Related party transaction [Line Items]
Related party description of transaction		MGE sold a parcel of land in Middleton, Wisconsin to ATC
ATC [Member]
Related party transaction [Line Items]
Related party description of transaction		MGE sold a parcel of land in Middleton, Wisconsin to ATC
Related party amounts of transactions		2,700,000
Gain from related party transactions		2,600,000
MGE Transco [Member] | ATC [Member]
Equity method investments [Line Items]
Equity earnings in ATC	8,600,000	8,500,000	8,200,000
Dividend income from ATC	6,700,000	6,700,000	6,300,000
Contributions to ATC	$ 900,000	$ 700,000	$ 3,600,000
MGE Transco ownership interest in ATC	3.60%	3.60%