Taxes (Details) (USD $) In Millions, unless otherwise specified			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2011 MGE Energy [Member]	Sep. 30, 2010 MGE Energy [Member]	Sep. 30, 2011 MGE Energy [Member]	Sep. 30, 2010 MGE Energy [Member]	Sep. 30, 2011 MGE [Member]	Sep. 30, 2010 MGE [Member]	Sep. 30, 2011 MGE [Member]	Sep. 30, 2010 MGE [Member]
Unrecognized Tax Benefits That Would Impact Effective Tax Rate [Abstract]
Total unrecognized tax benefit	$ 5.2	$ 4.4
Effective Income Tax Rate [Line Items]
Effective income tax rate			37.30%	39.50%	37.30%	37.80%	37.10%	39.50%	37.30%	37.80%