Investments (Details-2) - USD ($) $ in Thousands				12 Months Ended
	Jan. 31, 2017	Jan. 10, 2017	Dec. 01, 2016	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment in ATC				$ 8,428		$ 7,728	$ 9,150
Dividend income from ATC				7,926		6,645	7,740
Capital contributions to investments				2,958		1,053	2,185
MGE Transco [Member] | ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment in ATC				8,670		7,728	9,150
Dividend income from ATC				7,926	[1]	6,645	7,740
Capital contributions to investments				$ 2,486		$ 710	1,775
Ownership interest in equity-method investee				3.60%		3.60%
Dividend receivable from ATC				$ 2,100
MGE Transco [Member] | ATC [Member] | Subsequent Event [Member]
Schedule Of Equity Method Investments [Line Items]
Capital contributions to investments	$ 1,400
MGEE Transco [Member] | ATC Holdco [Member]
Schedule Of Equity Method Investments [Line Items]
Ownership interest in equity-method investee				4.00%
MGEE Transco [Member] | ATC Holdco [Member] | Subsequent Event [Member]
Schedule Of Equity Method Investments [Line Items]
Capital contributions to investments		$ 200
MGE [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment in ATC				$ 6,366		$ 7,728	9,150
Dividend income from ATC				5,032		6,645	7,740
Capital contributions to investments				1,598		710	1,775
Dividend in kind to parent			$ 15,800	15,822		0	0
MGE Energy [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings from investment in ATC				$ 75,581		$ 71,306	$ 81,811
Dividend in kind to parent			$ (15,800)

[1] As of December 31, 2016, MGE Transco recorded a $2.1 million receivable from ATC for a cash dividend received in January 2017.