Madison Gas and Electric Company Comprehensive Income (Details) (MGE [Member], USD $) In Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
MGE [Member]
Other Comprehensive Income [Line Items]
Net Income	$ 21,092	$ 20,101	$ 51,770	$ 46,049
Unrealized gain (loss) on available-for-sale securities, net of tax	(52)	4	(20)	(48)
Reclassification of realized gain on available-for-sale securities, net of tax	0	0	(15)	0
Total comprehensive income including noncontrolling interest	21,040	20,105	51,735	46,001
Less: Comprehensive income attributable to noncontrolling interest	(6,010)	(5,108)	(17,935)	(15,104)
Total comprehensive income	15,030	14,997	33,800	30,897
Other Comprehensive Income Taxes
Unrealized gain (loss) on available-for-sale securities, taxes	(35)	2	(14)	(32)
Reclassification of realized gain on available-for-sale securities, taxes	$ 0	$ 0	$ (10)	$ 0

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