Madison Gas and Electric Company Comprehensive Income (Details) (MGE [Member], USD $) In Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
MGE [Member]
Other Comprehensive Income [Line Items]
Net Income	$ 12,811	$ 11,725	$ 30,678	$ 25,948
Unrealized gain (loss) on available-for-sale securities, net of tax	(3)	(65)	32	(51)
Reclassification of realized gain on available-for-sale securities, net of tax	(15)	0	(15)	0
Total comprehensive income including noncontrolling interest	12,793	11,660	30,695	25,897
Less: Comprehensive income attributable to noncontrolling interest	(5,992)	(4,900)	(11,925)	(9,996)
Total comprehensive income	6,801	6,760	18,770	15,901
Other Comprehensive Income Taxes
Unrealized gain (loss) on available-for-sale securities, taxes	(2)	(43)	21	(34)
Reclassification of realized gain on available-for-sale securities, taxes	$ (10)	$ 0	$ (10)	$ 0

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