Taxes (Details) (USD $) In Millions, unless otherwise specified			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2011 MGE Energy [Member]	Jun. 30, 2010 MGE Energy [Member]	Jun. 30, 2011 MGE Energy [Member]	Jun. 30, 2010 MGE Energy [Member]	Jun. 30, 2011 MGE [Member]	Jun. 30, 2010 MGE [Member]	Jun. 30, 2011 MGE [Member]	Jun. 30, 2010 MGE [Member]
Unrecognized Tax Benefits That Would Impact Effective Tax Rate [Abstract]
Liability for tax uncertainty	$ 0.6
Total unrecognized tax benefit	$ 5.0	$ 4.4
Effective Income Tax Rate [Line Items]
Effective income tax rate			37.30%	35.90%	37.40%	36.40%	37.30%	36.00%	37.40%	36.40%