Segment Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Operating revenues	$ 135,211,000	$ 138,198,000	$ 402,124,000	$ 427,914,000
Equity in earnings of investment			7,780,000	6,879,000
Net Income Including Noncontrolling Interest	31,794,000	30,657,000	76,622,000	70,212,000
Net Income	31,794,000	30,657,000	76,622,000	70,212,000
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	116,354,000	120,607,000	303,090,000	314,886,000
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	18,643,000	17,377,000	98,568,000	112,547,000
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	214,000	214,000	466,000	481,000
Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	135,211,000	138,198,000	402,124,000	427,914,000
Equity in earnings of investment	2,353,000	2,372,000	7,780,000	6,808,000
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	116,563,000	120,832,000	303,674,000	315,508,000
Equity in earnings of investment	0	0	0	0
Net Income	24,761,000	23,681,000	46,439,000	40,905,000
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	22,137,000	23,056,000	107,868,000	125,118,000
Equity in earnings of investment	0	0	0	0
Net Income	221,000	(61,000)	9,216,000	8,648,000
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,316,000	10,233,000	30,714,000	30,468,000
Equity in earnings of investment	0	0	0	0
Net Income	5,251,000	5,131,000	15,536,000	15,211,000
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Equity in earnings of investment	2,353,000	2,372,000	7,780,000	6,808,000
Net Income	1,710,000	1,726,000	5,659,000	4,952,000
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Equity in earnings of investment	0	0	0	0
Net Income	(149,000)	180,000	(228,000)	496,000
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(13,805,000)	(15,923,000)	(40,132,000)	(43,180,000)
Equity in earnings of investment	0	0	0	0
Net Income	0	0	0	0
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	209,000	225,000	584,000	622,000
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,494,000	5,679,000	9,300,000	12,571,000
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,102,000	10,019,000	30,248,000	29,987,000
Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Consolidation Elimination Entries [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues	135,211,000	138,198,000	402,124,000	427,914,000
Net Income Including Noncontrolling Interest	30,233,000	28,751,000	71,191,000	64,764,000
Less Net Income Attributable to Noncontrolling Interest, net of tax	(5,493,000)	(5,614,000)	(16,754,000)	(16,725,000)
Net Income	24,740,000	23,137,000	54,437,000	48,039,000
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	116,354,000	120,607,000	303,090,000	314,886,000
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	18,643,000	17,377,000	98,568,000	112,547,000
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	214,000	214,000	466,000	481,000
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	135,211,000	138,198,000	402,124,000	427,914,000
Net Income	24,740,000	23,137,000	54,437,000	48,039,000
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	116,563,000	120,832,000	303,674,000	315,508,000
Net Income	24,761,000	23,681,000	46,439,000	40,905,000
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	22,137,000	23,056,000	107,868,000	125,118,000
Net Income	221,000	(61,000)	9,216,000	8,648,000
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,316,000	10,233,000	30,714,000	30,468,000
Net Income	5,251,000	5,131,000	15,536,000	15,211,000
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(13,805,000)	(15,923,000)	(40,132,000)	(43,180,000)
Net Income	(5,493,000)	(5,614,000)	(16,754,000)	(16,725,000)
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	209,000	225,000	584,000	622,000
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,494,000	5,679,000	9,300,000	12,571,000
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 10,102,000	$ 10,019,000	$ 30,248,000	$ 29,987,000