Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Segment Reporting Information [Line Items]
Operating revenues	$ 145,873	$ 135,211	$ 444,518	$ 402,124
Equity in earnings of investment			7,440	7,780
Net income (loss)	34,917	31,794	92,701	76,622
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	121,639	116,354	324,110	303,090
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	24,020	18,643	119,944	98,568
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	214	214	464	466
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	145,873	135,211	444,518	402,124
Equity in earnings of investment	2,532	2,353	7,440	7,780
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	121,728	116,563	324,426	303,674
Equity in earnings of investment	0	0	0	0
Net income (loss)	27,833	24,761	59,979	46,439
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	30,709	22,137	134,321	107,868
Equity in earnings of investment	0	0	0	0
Net income (loss)	(218)	221	11,615	9,216
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,438	10,316	31,059	30,714
Equity in earnings of investment	0	0	0	0
Net income (loss)	5,386	5,251	15,935	15,536
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0	0	0
Equity in earnings of investment	2,532	2,353	7,440	7,780
Net income (loss)	1,842	1,710	5,413	5,659
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 (loss)	74	(149)	(241)	(228)
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(17,002)	(13,805)	(45,288)	(40,132)
Equity in earnings of investment	0	0	0	0
Net income (loss)	0	0	0	0
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	89	209	316	584
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	6,689	3,494	14,377	9,300
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,224	10,102	30,595	30,248
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	145,873	135,211	444,518	402,124
Net income (loss)	27,374	24,740	70,774	54,437
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	121,639	116,354	324,110	303,090
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	24,020	18,643	119,944	98,568
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	214	214	464	466
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	145,873	135,211	444,518	402,124
Net income (loss)	27,374	24,740	70,774	54,437
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	121,728	116,563	324,426	303,674
Net income (loss)	27,833	24,761	59,979	46,439
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	30,709	22,137	134,321	107,868
Net income (loss)	(218)	221	11,615	9,216
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,438	10,316	31,059	30,714
Net income (loss)	5,386	5,251	15,935	15,536
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(17,002)	(13,805)	(45,288)	(40,132)
Net income (loss)	(5,627)	(5,493)	(16,755)	(16,754)
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	89	209	316	584
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	6,689	3,494	14,377	9,300
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 10,224	$ 10,102	$ 30,595	$ 30,248