Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Operating revenues	$ 149,873	$ 167,569
Equity in earnings of investment	2,266	2,218
Net Income Including Noncontrolling Interest	26,037	24,007
Net Income	26,037	24,007
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	92,990	97,416
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	56,845	70,100
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	38	53
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	149,873	167,569
Equity in earnings of investment	2,286	2,168
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	93,181	97,615
Equity in earnings of investment	0	0
Net Income	11,463	9,349
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	60,296	75,062
Equity in earnings of investment	0	0
Net Income	8,034	7,760
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,094	10,026
Equity in earnings of investment	0	0
Net Income	5,060	4,961
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Equity in earnings of investment	2,286	2,168
Net Income	1,663	1,577
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Equity in earnings of investment	0	0
Net Income	(183)	360
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(13,698)	(15,134)
Equity in earnings of investment	0	0
Net Income	0	0
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	191	199
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,451	4,962
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,056	9,973
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	149,873	167,569
Net Income Including Noncontrolling Interest	24,557	22,070
Less Net Income Attributable to Noncontrolling Interest, net of tax	(5,493)	(5,490)
Net Income	19,064	16,580
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	92,990	97,416
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	56,845	70,100
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	38	53
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	149,873	167,569
Net Income	19,064	16,580
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	93,181	97,615
Net Income	11,463	9,349
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	60,296	75,062
Net Income	8,034	7,760
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,094	10,026
Net Income	5,060	4,961
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(13,698)	(15,134)
Net Income	(5,493)	(5,490)
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	191	199
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,451	4,962
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 10,056	$ 9,973