Segment Information (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2025 USD ($) Segment	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Segment Reporting Information [Line Items]
Operating revenues		$ 743,654	$ 676,944	$ 690,431
Depreciation and amortization		(114,324)	(108,581)	(100,352)
Operating Income (Loss)		170,653	146,262	146,385
Interest (expense) income, net		(33,799)	(32,930)	(30,429)
Income tax (provision) benefit		(20,765)	(10,596)	(27,803)
Equity earnings of investments		13,009	12,275	10,631
Net Income		135,889	120,569	117,699
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets		$ 343,220	236,925	222,071
Number of Reportable Segments | Segment		4
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		$ 531,554	497,673	489,729
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		211,423	178,587	200,012
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		677	684	690
Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0
All Others [Members]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		743,654	676,944	690,431
Fuel and purchased power		(90,851)	(86,846)	(98,851)
Purchased gas costs		(107,026)	(82,693)	(106,647)
Depreciation and amortization		(114,324)	(108,581)	(100,352)
Interest expense		(37,942)	(36,352)	(33,091)
Other segment items	[1]	(249,866)	(243,582)	(216,619)
Income tax (provision) benefit		(20,765)	(10,596)	(27,803)
Equity earnings of investments		13,009	12,275	10,631
Net Income		135,889	120,569	117,699
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		531,478	497,479	490,651
Fuel and purchased power		(95,150)	(90,726)	(102,520)
Purchased gas costs		0	0	0
Depreciation and amortization		(89,212)	(84,264)	(77,440)
Interest expense		(27,035)	(25,616)	(22,883)
Other segment items	[1]	(232,227)	(225,985)	(201,680)
Income tax (provision) benefit		(2,077)	3,620	(10,182)
Equity earnings of investments		0	0	0
Net Income		85,777	74,508	75,946
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets		285,576	192,469	180,743
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		232,299	193,570	215,513
Fuel and purchased power		0	0	0
Purchased gas costs		(123,648)	(93,834)	(118,509)
Depreciation and amortization		(17,376)	(16,779)	(15,531)
Interest expense		(7,388)	(6,943)	(6,146)
Other segment items	[1]	(61,630)	(60,290)	(54,084)
Income tax (provision) benefit		(6,000)	(1,995)	(7,175)
Equity earnings of investments		0	0	0
Net Income		16,257	13,729	14,068
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets		48,003	38,101	36,402
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		45,420	44,515	42,276
Fuel and purchased power		0	0	0
Purchased gas costs		0	0	0
Depreciation and amortization		(7,736)	(7,538)	(7,381)
Interest expense		(3,519)	(3,793)	(4,062)
Other segment items	[1]	(131)	(113)	(107)
Income tax (provision) benefit		(9,271)	(9,009)	(8,370)
Equity earnings of investments		0	0	0
Net Income		24,763	24,062	22,356
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets		9,641	6,355	4,926
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0
Fuel and purchased power		0	0	0
Purchased gas costs		0	0	0
Depreciation and amortization		0	0	0
Interest expense		0	0	0
Other segment items	[1]	0	0	2
Income tax (provision) benefit		(3,545)	(3,345)	(2,897)
Equity earnings of investments		13,009	12,275	10,631
Net Income		9,464	8,930	7,736
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets		0	0	0
Operating Segments [Member] | Total Reportable Segments
Segment Reporting Information [Line Items]
Operating revenues		809,197	735,564	748,440
Fuel and purchased power		(95,150)	(90,726)	(102,520)
Purchased gas costs		(123,648)	(93,834)	(118,509)
Depreciation and amortization		(114,324)	(108,581)	(100,352)
Interest expense		(37,942)	(36,352)	(33,091)
Other segment items	[1]	(293,988)	(286,388)	(255,869)
Income tax (provision) benefit		(20,893)	(10,729)	(28,624)
Equity earnings of investments		13,009	12,275	10,631
Net Income		136,261	121,229	120,106
Operating Segments [Member] | All Others [Members]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0
Fuel and purchased power		0	0	0
Purchased gas costs		0	0	0
Depreciation and amortization		0	0	0
Interest expense		0	0	0
Other segment items	[1]	(500)	(793)	(3,228)
Income tax (provision) benefit		128	133	821
Equity earnings of investments		0	0	0
Net Income		(372)	(660)	(2,407)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets		0	0	0
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(65,543)	(58,620)	(58,009)
Fuel and purchased power		4,299	3,880	3,669
Purchased gas costs		16,622	11,141	11,862
Depreciation and amortization		0	0	0
Interest expense		0	0	0
Other segment items	[1]	44,622	43,599	42,478
Income tax (provision) benefit		0	0	0
Equity earnings of investments		0	0	0
Net Income		0	0	0
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets		0	0	0
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		(76)	(194)	922
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		20,876	14,983	15,501
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		44,743	43,831	41,586
Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0
Consolidation Elimination Entries [Member] | Total Reportable Segments
Segment Reporting Information [Line Items]
Operating revenues		65,543	58,620	58,009
Consolidation Elimination Entries [Member] | All Others [Members]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues		743,654	676,944	690,431
Depreciation and amortization		(114,324)	(108,581)	(100,352)
Operating Income (Loss)		171,698	147,167	147,383
Interest (expense) income, net		(34,102)	(33,369)	(30,651)
Income tax (provision) benefit		(17,348)	(7,384)	(25,727)
Net income attributable to noncontrolling interest, net of tax		22,652	22,855	21,868
Net Income		104,145	89,444	90,502
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets		$ 343,220	236,925	222,071
Number of Reportable Segments | Segment		3
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		$ 531,554	497,673	489,729
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		211,423	178,587	200,012
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		677	684	690
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		743,654	676,944	690,431
Fuel and purchased power		(90,851)	(86,846)	(98,851)
Purchased gas costs		(107,026)	(82,693)	(106,647)
Depreciation and amortization		(114,324)	(108,581)	(100,352)
Interest expense		(37,942)	(36,352)	(33,091)
Other segment items	[2]	(249,366)	(242,789)	(213,393)
Income tax (provision) benefit		(17,348)	(7,384)	(25,727)
Net income attributable to noncontrolling interest, net of tax		(22,652)	(22,855)	(21,868)
Net Income		104,145	89,444	90,502
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		531,478	497,479	490,651
Fuel and purchased power		(95,150)	(90,726)	(102,520)
Purchased gas costs		0	0	0
Depreciation and amortization		(89,212)	(84,264)	(77,440)
Interest expense		(27,035)	(25,616)	(22,883)
Other segment items	[2]	(232,227)	(225,985)	(201,680)
Income tax (provision) benefit		(2,077)	3,620	(10,182)
Net income attributable to noncontrolling interest, net of tax		0	0	0
Net Income		85,777	74,508	75,946
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets		285,576	192,469	180,743
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		232,299	193,570	215,513
Fuel and purchased power		0	0	0
Purchased gas costs		(123,648)	(93,834)	(118,509)
Depreciation and amortization		(17,376)	(16,779)	(15,531)
Interest expense		(7,388)	(6,943)	(6,146)
Other segment items	[2]	(61,630)	(60,290)	(54,084)
Income tax (provision) benefit		(6,000)	(1,995)	(7,175)
Net income attributable to noncontrolling interest, net of tax		0	0	0
Net Income		16,257	13,729	14,068
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets		48,003	38,101	36,402
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		45,420	44,515	42,276
Fuel and purchased power		0	0	0
Purchased gas costs		0	0	0
Depreciation and amortization		(7,736)	(7,538)	(7,381)
Interest expense		(3,519)	(3,793)	(4,062)
Other segment items	[2]	(131)	(113)	(107)
Income tax (provision) benefit		(9,271)	(9,009)	(8,370)
Net income attributable to noncontrolling interest, net of tax		0	0	0
Net Income		24,763	24,062	22,356
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets		9,641	6,355	4,926
MGE [Member] | Operating Segments [Member] | Total Reportable Segments
Segment Reporting Information [Line Items]
Operating revenues		809,197	735,564	748,440
Fuel and purchased power		(95,150)	(90,726)	(102,520)
Purchased gas costs		(123,648)	(93,834)	(118,509)
Depreciation and amortization		(114,324)	(108,581)	(100,352)
Interest expense		(37,942)	(36,352)	(33,091)
Other segment items	[2]	(293,988)	(286,388)	(255,871)
Income tax (provision) benefit		(17,348)	(7,384)	(25,727)
Net income attributable to noncontrolling interest, net of tax		0	0	0
Net Income		126,797	112,299	112,370
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(65,543)	(58,620)	(58,009)
Fuel and purchased power		4,299	3,880	3,669
Purchased gas costs		16,622	11,141	11,862
Depreciation and amortization		0	0	0
Interest expense		0	0	0
Other segment items	[2]	44,622	43,599	42,478
Income tax (provision) benefit		0	0	0
Net income attributable to noncontrolling interest, net of tax		(22,652)	(22,855)	(21,868)
Net Income		(22,652)	(22,855)	(21,868)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets		0	0	0
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		(76)	(194)	922
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		20,876	14,983	15,501
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		44,743	43,831	41,586
MGE [Member] | Consolidation Elimination Entries [Member] | Total Reportable Segments
Segment Reporting Information [Line Items]
Operating revenues		$ 65,543	$ 58,620	$ 58,009

[1] Other segment items include AFUDC Income, Other Income, Net, Other Operations and Maintenance, Other General Taxes, and Interest Revenue.

[2] Other segment items include AFUDC Income, Other Income, Net, Other Operations and Maintenance, Other General Taxes, and Interest Revenue.