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Investment in ATC (Details-1) (USD $)	3 Months Ended		0 Months Ended
Investment in ATC (Details-1) (USD $)	Mar. 31, 2015	Mar. 31, 2014	Apr. 30, 2015	Dec. 31, 2014
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment	$ 1,881,000	$ 2,481,000
Dividend income from investment	1,420,000	1,917,000
Capital contributions to investment	280,000	693,000
MGE Transco [Member] \| ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment	1,881,000	2,481,000
Dividend income from investment	1,420,000	1,917,000
Capital contributions to investment	178,000	533,000
Equity method investment	68,300,000			67,700,000
MGE Transco [Member] \| ATC [Member] \| Subsequent Event [Member]
Schedule Of Equity Method Investments [Line Items]
Capital contributions to investment			$ 200,000