Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Operating revenues	$ 167,915	$ 149,873
Equity in earnings of investment	2,444	2,266
Net Income	34,933	26,037
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	100,609	92,990
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	67,270	56,845
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	36	38
Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	167,915	149,873
Equity in earnings of investment	2,444	2,286
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	100,882	93,181
Equity in earnings of investment	0	0
Net Income	18,024	11,463
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	72,081	60,296
Equity in earnings of investment	0	0
Net Income	10,556	8,034
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,209	10,094
Equity in earnings of investment	0	0
Net Income	5,194	5,060
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Equity in earnings of investment	2,444	2,286
Net Income	1,778	1,663
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Equity in earnings of investment	0	0
Net Income	(619)	(183)
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(15,257)	(13,698)
Equity in earnings of investment	0	0
Net Income	0	0
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	273	191
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	4,811	3,451
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,173	10,056
Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Consolidation Elimination Entries [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues	167,915	149,873
Net Income	28,273	19,064
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	100,609	92,990
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	67,270	56,845
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	36	38
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	167,915	149,873
Net Income	28,273	19,064
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	100,882	93,181
Net Income	18,024	11,463
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	72,081	60,296
Net Income	10,556	8,034
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,209	10,094
Net Income	5,194	5,060
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(15,257)	(13,698)
Net Income	(5,501)	(5,493)
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	273	191
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	4,811	3,451
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 10,173	$ 10,056