Investments (Details-2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Schedule Of Equity Method Investments [Line Items]
Equity earnings of investments	$ 9,889	$ 8,821		$ 10,125
Dividends from investment	7,347	6,958		8,803
Capital contributions to investments	7,813	5,926		11,081
MGE Energy [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings of investments	87,728	85,220		99,246
MGE Transco [Member] | ATC [Member]
Schedule Of Equity Method Investments [Line Items]
Equity earnings of investments	9,889	8,821		10,125
Dividends from investment	7,347	4,611	[1]	9,078	[1]
Capital contributions to investments	$ 3,018	$ 2,841		3,551
Ownership interest in equity-method investee	3.60%	3.60%
Dividend receivable from ATC				2,300
MGEE Transco [Member] | ATC Holdco [Member]
Schedule Of Equity Method Investments [Line Items]
Capital contributions to investments	$ 100	$ 300		$ 2,900
Ownership interest in equity-method investee	4.40%	4.40%

[1] MGE Transco recorded a $2.3 million dividend receivable from ATC as of December 31, 2017. A cash dividend was received in January of 2018.