Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Segment Reporting Information [Line Items]
Operating revenues		$ 175,679	$ 168,480	$ 554,101	$ 505,529
Depreciation and amortization		(28,816)	(27,104)	(84,848)	(80,636)
Income tax (provision) benefit		(7,789)	(3,644)	(17,060)	(7,924)
Equity in earnings of investment				9,586	8,427
Net Income (Loss)		44,497	40,939	112,587	98,547
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets				255,622	164,064
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		155,277	147,790	410,044	384,298
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		20,188	20,476	143,594	120,761
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		214	214	463	470
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		175,679	168,480	554,101	505,529
Fuel and purchased power		(26,478)	(25,379)	(70,279)	(67,612)
Purchased gas costs		(4,865)	(4,628)	(70,142)	(52,798)
Depreciation and amortization		(28,816)	(27,104)	(84,848)	(80,636)
Interest expense		(9,412)	(9,230)	(27,716)	(27,231)
Other segment items	[1]	(57,167)	(60,457)	(181,055)	(179,208)
Income tax (provision) benefit		(7,789)	(3,644)	(17,060)	(7,924)
Equity in earnings of investment		3,345	2,901	9,586	8,427
Net Income (Loss)		44,497	40,939	112,587	98,547
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		155,179	147,746	409,870	384,144
Fuel and purchased power		(27,878)	(26,679)	(73,508)	(70,590)
Purchased gas costs		0	0	0	0
Depreciation and amortization		(22,470)	(21,016)	(66,099)	(62,553)
Interest expense		(6,703)	(6,519)	(19,681)	(19,170)
Other segment items	[1]	(56,785)	(56,480)	(170,894)	(167,283)
Income tax (provision) benefit		(5,039)	(2,017)	(3,609)	1,910
Equity in earnings of investment		0	0	0	0
Net Income (Loss)		36,304	35,035	76,079	66,458
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets				210,095	127,712
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		26,581	24,683	159,017	132,352
Fuel and purchased power		0	0	0	0
Purchased gas costs		(9,868)	(7,546)	(82,369)	(61,439)
Depreciation and amortization		(4,396)	(4,196)	(12,975)	(12,441)
Interest expense		(1,836)	(1,771)	(5,367)	(5,190)
Other segment items	[1]	(14,439)	(14,777)	(45,550)	(43,940)
Income tax (provision) benefit		1,148	1,581	(3,278)	(704)
Equity in earnings of investment		0	0	0	0
Net Income (Loss)		(2,810)	(2,026)	9,478	8,638
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets				36,396	31,173
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,463	11,266	33,937	33,295
Fuel and purchased power		0	0	0	0
Purchased gas costs		0	0	0	0
Depreciation and amortization		(1,950)	(1,892)	(5,774)	(5,642)
Interest expense		(873)	(940)	(2,668)	(2,871)
Other segment items	[1]	(30)	(48)	(97)	(87)
Income tax (provision) benefit		(2,345)	(2,285)	(6,918)	(6,727)
Equity in earnings of investment		0	0	0	0
Net Income (Loss)		6,265	6,101	18,480	17,968
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets				9,131	5,179
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0	0
Fuel and purchased power		0	0	0	0
Purchased gas costs		0	0	0	0
Depreciation and amortization		0	0	0	0
Interest expense		0	0	0	0
Other segment items	[1]	0	0	(0)	0
Income tax (provision) benefit		(912)	(789)	(2,614)	(2,297)
Equity in earnings of investment		3,345	2,901	9,586	8,427
Net Income (Loss)		2,433	2,112	6,972	6,130
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets				0	0
Operating Segments [Member] | Total Reportable Segments
Segment Reporting Information [Line Items]
Operating revenues		193,223	183,695	602,824	549,791
Fuel and purchased power		(27,878)	(26,679)	(73,508)	(70,590)
Purchased gas costs		(9,868)	(7,546)	(82,369)	(61,439)
Depreciation and amortization		(28,816)	(27,104)	(84,848)	(80,636)
Interest expense		(9,412)	(9,230)	(27,716)	(27,231)
Other segment items	[1]	(71,254)	(71,305)	(216,541)	(211,310)
Income tax (provision) benefit		(7,148)	(3,510)	(16,419)	(7,818)
Equity in earnings of investment		3,345	2,901	9,586	8,427
Net Income (Loss)		42,192	41,222	111,009	99,194
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0	0
Fuel and purchased power		0	0	0	0
Purchased gas costs		0	0	0	0
Depreciation and amortization		0	0	0	0
Interest expense		0	0	0	0
Other segment items	[1]	2,946	(149)	2,219	(541)
Income tax (provision) benefit		(641)	(134)	(641)	(106)
Equity in earnings of investment		0	0	0	0
Net Income (Loss)		2,305	(283)	1,578	(647)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets				0	0
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(17,544)	(15,215)	(48,723)	(44,262)
Fuel and purchased power		1,400	1,300	3,229	2,978
Purchased gas costs		5,003	2,918	12,227	8,641
Depreciation and amortization		0	0	0	0
Interest expense		0	0	0	0
Other segment items	[1]	11,141	10,997	33,267	32,643
Income tax (provision) benefit		0	0	0	0
Equity in earnings of investment		0	0	0	0
Net Income (Loss)		0	0	0	0
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets				0	0
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		(98)	(44)	(174)	(154)
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		6,393	4,207	15,423	11,591
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,249	11,052	33,474	32,825
Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0	0
Consolidation Elimination Entries [Member] | Total Reportable Segments
Segment Reporting Information [Line Items]
Operating revenues		17,544	15,215	48,723	44,262
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		175,679	168,480	554,101	505,529
Depreciation and amortization		(28,816)	(27,104)	(84,848)	(80,636)
Income tax (provision) benefit		(6,236)	(2,720)	(13,805)	(5,522)
Net Income (Loss) Attributable to Noncontrolling Interest		5,668	5,777	16,981	17,140
Net Income (Loss)		34,091	33,333	87,056	75,924
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets				255,622	164,064
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		155,277	147,790	410,044	384,298
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		20,188	20,476	143,594	120,761
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		214	214	463	470
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		175,679	168,480	554,101	505,529
Fuel and purchased power		(26,478)	(25,379)	(70,279)	(67,612)
Purchased gas costs		(4,865)	(4,628)	(70,142)	(52,798)
Depreciation and amortization		(28,816)	(27,104)	(84,848)	(80,636)
Interest expense		(9,412)	(9,230)	(27,716)	(27,230)
Other segment items	[2]	(60,113)	(60,309)	(183,274)	(178,667)
Income tax (provision) benefit		(6,236)	(2,720)	(13,805)	(5,522)
Net Income (Loss) Attributable to Noncontrolling Interest		(5,668)	(5,777)	(16,981)	(17,140)
Net Income (Loss)		34,091	33,333	87,056	75,924
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		155,179	147,746	409,870	384,144
Fuel and purchased power		(27,878)	(26,679)	(73,508)	(70,590)
Purchased gas costs		0	0	0	0
Depreciation and amortization		(22,470)	(21,016)	(66,099)	(62,553)
Interest expense		(6,703)	(6,519)	(19,681)	(19,169)
Other segment items	[2]	(56,785)	(56,480)	(170,894)	(167,283)
Income tax (provision) benefit		(5,039)	(2,017)	(3,609)	1,909
Net Income (Loss) Attributable to Noncontrolling Interest		0	0	0	0
Net Income (Loss)		36,304	35,035	76,079	66,458
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets				210,095	127,712
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		26,581	24,683	159,017	132,352
Fuel and purchased power		0	0	0	0
Purchased gas costs		(9,868)	(7,546)	(82,369)	(61,439)
Depreciation and amortization		(4,396)	(4,196)	(12,975)	(12,441)
Interest expense		(1,836)	(1,771)	(5,367)	(5,190)
Other segment items	[2]	(14,439)	(14,778)	(45,550)	(43,940)
Income tax (provision) benefit		1,148	1,582	(3,278)	(704)
Net Income (Loss) Attributable to Noncontrolling Interest		0	0	0	0
Net Income (Loss)		(2,810)	(2,026)	9,478	8,638
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets				36,396	31,173
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,463	11,266	33,937	33,295
Fuel and purchased power		0	0	0	0
Purchased gas costs		0	0	0	0
Depreciation and amortization		(1,950)	(1,892)	(5,774)	(5,642)
Interest expense		(873)	(940)	(2,668)	(2,871)
Other segment items	[2]	(30)	(48)	(97)	(87)
Income tax (provision) benefit		(2,345)	(2,285)	(6,918)	(6,727)
Net Income (Loss) Attributable to Noncontrolling Interest		0	0	0	0
Net Income (Loss)		6,265	6,101	18,480	17,968
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets				9,131	5,179
MGE [Member] | Operating Segments [Member] | Total Reportable Segments
Segment Reporting Information [Line Items]
Operating revenues		193,223	183,695	602,824	549,791
Fuel and purchased power		(27,878)	(26,679)	(73,508)	(70,590)
Purchased gas costs		(9,868)	(7,546)	(82,369)	(61,439)
Depreciation and amortization		(28,816)	(27,104)	(84,848)	(80,636)
Interest expense		(9,412)	(9,230)	(27,716)	(27,230)
Other segment items	[2]	(71,254)	(71,306)	(216,541)	(211,310)
Income tax (provision) benefit		(6,236)	(2,720)	(13,805)	(5,522)
Net Income (Loss) Attributable to Noncontrolling Interest		0	0	0	0
Net Income (Loss)		39,759	39,110	104,037	93,064
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(17,544)	(15,215)	(48,723)	(44,262)
Fuel and purchased power		1,400	1,300	3,229	2,978
Purchased gas costs		5,003	2,918	12,227	8,641
Depreciation and amortization		0	0	0	0
Interest expense		0	0	0	0
Other segment items	[2]	11,141	10,997	33,267	32,643
Income tax (provision) benefit		0	0	0	0
Net Income (Loss) Attributable to Noncontrolling Interest		(5,668)	(5,777)	(16,981)	(17,140)
Net Income (Loss)		(5,668)	(5,777)	(16,981)	(17,140)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets				0	0
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		(98)	(44)	(174)	(154)
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		6,393	4,207	15,423	11,591
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,249	11,052	33,474	32,825
MGE [Member] | Consolidation Elimination Entries [Member] | Total Reportable Segments
Segment Reporting Information [Line Items]
Operating revenues		$ 17,544	$ 15,215	$ 48,723	$ 44,262

[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.