Investment in ATC (Details-2) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Minority Interest [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 Energy [Member]
Minority Interest [Line Items]
MGE Energy's ownership interest in MGE Transco		50.50%		50.50%
MGE [Member]
Minority Interest [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's ownership interest in MGE Transco		49.50%		49.50%
Noncontrolling interest on balance sheet		$ 116,206		$ 116,206		$ 140,308
MGE [Member] | Noncontrolling Interest [Member] | MGE Transco [Member]
Minority Interest [Line Items]
Equity earnings from investment	[1]	254	679	1,410	1,848
Dividends received from investment	[1]	561	423	1,113	1,007
Capital contributions to investments		$ 888	$ 177	$ 1,598	$ 533
Noncontrolling interest on balance sheet						$ 23,600

[1] Amounts reflected net of tax.