Segment Information (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Operating revenues	$ 117,040,000	$ 122,147,000	$ 266,913,000	$ 289,716,000
Equity in earnings of investment	3,139,000	2,297,000	5,405,000	4,515,000
Net Income Including Noncontrolling Interest	18,791,000	15,548,000	44,828,000	39,554,000
Net Income	18,791,000	15,548,000	44,828,000	39,554,000
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	93,747,000	96,863,000	186,737,000	194,279,000
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	23,079,000	25,070,000	79,924,000	95,170,000
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	214,000	214,000	252,000	267,000
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	117,040,000	122,147,000	266,913,000	289,716,000
Equity in earnings of investment	3,141,000	2,267,000	5,427,000	4,436,000
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	93,932,000	97,061,000	187,112,000	194,676,000
Equity in earnings of investment	0	0	0	0
Net Income	10,216,000	7,876,000	21,679,000	17,226,000
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	25,434,000	26,999,000	85,730,000	102,061,000
Equity in earnings of investment	0	0	0	0
Net Income	960,000	951,000	8,994,000	8,710,000
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,303,000	10,209,000	20,398,000	20,235,000
Equity in earnings of investment	0	0	0	0
Net Income	5,225,000	5,116,000	10,285,000	10,077,000
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Equity in earnings of investment	3,141,000	2,267,000	5,427,000	4,436,000
Net Income	2,285,000	1,648,000	3,948,000	3,226,000
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	105,000	(43,000)	(78,000)	315,000
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(12,629,000)	(12,122,000)	(26,327,000)	(27,256,000)
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	185,000	198,000	375,000	397,000
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,355,000	1,929,000	5,806,000	6,891,000
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,089,000	9,995,000	20,146,000	19,968,000
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	117,040,000	122,147,000	266,913,000	289,716,000
Net Income Including Noncontrolling Interest	16,401,000	13,943,000	40,958,000	36,013,000
Less Net Income Attributable to Noncontrolling Interest, net of tax	(5,768,000)	(5,621,000)	(11,261,000)	(11,111,000)
Net Income	10,633,000	8,322,000	29,697,000	24,902,000
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	93,747,000	96,863,000	186,737,000	194,279,000
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	23,079,000	25,070,000	79,924,000	95,170,000
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	214,000	214,000	252,000	267,000
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	117,040,000	122,147,000	266,913,000	289,716,000
Net Income	10,633,000	8,322,000	29,697,000	24,902,000
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	93,932,000	97,061,000	187,112,000	194,676,000
Net Income	10,216,000	7,876,000	21,679,000	17,226,000
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	25,434,000	26,999,000	85,730,000	102,061,000
Net Income	960,000	951,000	8,994,000	8,710,000
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,303,000	10,209,000	20,398,000	20,235,000
Net Income	5,225,000	5,116,000	10,285,000	10,077,000
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(12,629,000)	(12,122,000)	(26,327,000)	(27,256,000)
Net Income	(5,768,000)	(5,621,000)	(11,261,000)	(11,111,000)
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	185,000	198,000	375,000	397,000
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,355,000	1,929,000	5,806,000	6,891,000
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 10,089,000	$ 9,995,000	$ 20,146,000	$ 19,968,000