Investment in ATC (Details-1) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment	$ 2,023	$ 2,398	$ 6,023	$ 6,568
Dividends received from investment	1,486	1,841	4,214	4,732
Capital contributions to investments	888	177	2,036	785
MGE Transco [Member] \| ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment	2,023	2,398	6,023	6,568
Dividends received from investment	1,486	1,841	4,214	4,732
Capital contributions to investments	888	177	1,598	533
Equity method investment	72,900		72,900		$ 69,500
MGE [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment	1,451	2,398	5,451	6,568
Dividends received from investment	1,486	1,841	4,214	4,732
Capital contributions to investments	888	$ 177	1,598	$ 533
MGE [Member] \| MGE Transco [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment	$ 46,800		$ 46,800

This item represents disclosure of the amount of dividends or other distributions received from unconsolidated subsidiaries, certain corporate joint ventures, and certain noncontrolled corporation; these investments are accounted for under the equity method of accounting. This element excludes distributions that constitute a return of investment, which are classified as investing activities.

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