Investment in ATC (Details-1) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment	$ 1,767	$ 2,289	$ 4,000	$ 4,170
Dividend income from investment	1,863	1,471	2,728	2,891
Contributions to investments	177	177	998	538
ATC [Member]
Related Party Transaction [Line Items]
Related party expenses	7,400	7,000	14,700	14,100
Due from related parties	200		200		$ 200
MGE Transco [Member] \| ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment	1,767	2,289	4,000	4,170
Dividend income from investment	1,863	1,471	2,728	2,891
Contributions to investments	177	177	710	355
Equity method investment	71,400		71,400		69,500
MGE [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment	1,767	2,289	4,000	4,170
Dividend income from investment	1,863	1,471	2,728	2,891
Contributions to investments	$ 177	$ 177	$ 710	$ 355
Minority Interest [Line Items]
MGE's ownership interest in MGE Transco	51.00%		51.00%
Noncontrolling interest on balance sheet	$ 142,670		$ 142,670		$ 140,308
MGE [Member] \| MGE Transco [Member]
Minority Interest [Line Items]
Noncontrolling interest on balance sheet	$ 24,900		$ 24,900
MGE Energy [Member]
Minority Interest [Line Items]
MGE Energy's ownership interest in MGE Transco	49.00%		49.00%

For an unclassified balance sheet, amounts due from related parties including affiliates, employees, joint ventures, officers and stockholders, immediate families thereof, and pension funds.

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