Investment in ATC (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Equity method investments [Line Items]
Investment in ATC	$ 55,800,000		$ 55,800,000		$ 54,200,000
Related Party Transactions [Abstract]
Related party decscription 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
Equity Method Investment Summarized Financial Data [Abstract]
Operating revenues	138,203,000	138,666,000	277,820,000	277,157,000
Operating expenses	(62,951,000)	(62,523,000)	(126,077,000)	(125,335,000)
Other expense, net	(134,000)	(621,000)	(492,000)	(819,000)
Interest expense, net	(19,479,000)	(21,467,000)	(41,376,000)	(41,831,000)
Earnings before members' income taxes	55,639,000	54,055,000	109,875,000	109,172,000
Mge Transco [Member]
Equity method investments [Line Items]
Equity earnings from investment in ATC			4,300,000	4,300,000
Dividend income from ATC			3,300,000	3,400,000
Contributions to ATC			$ 600,000	$ 500,000