Segment Information (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Operating revenues		$ 606,584	$ 538,633	$ 568,855
Depreciation and amortization		(76,983)	(74,188)	(71,562)
Operating Income (Loss)		117,294	109,997	110,910
Interest (expense) income, net		(24,112)	(23,521)	(23,063)
Income tax (provision) benefit		(4,115)	(19,423)	(19,784)
Equity earnings of investments		9,270	10,221	9,889
Net Income		105,761	92,418	86,874
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		2,371,906	2,253,651	2,081,664
Capital expenditures		153,169	203,139	164,036
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		420,286	393,692	408,285
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		185,620	144,261	159,875
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		678	680	695
Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0
All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		606,584	538,633	568,855
Depreciation and amortization		(76,983)	(74,188)	(71,562)
Operating Income (Loss)		117,294	109,997	110,910
Interest (expense) income, net		(24,112)	(23,521)	(23,063)
Income tax (provision) benefit		(4,115)	(19,423)	(19,784)
Equity earnings of investments		9,270	10,221	9,547
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		420,842	394,457	409,091
Depreciation and amortization		(56,672)	(54,658)	(52,755)
Operating Income (Loss)		58,993	57,847	59,180
Interest (expense) income, net		(15,261)	(14,446)	(14,978)
Income tax (provision) benefit		10,672	(4,230)	(5,037)
Equity earnings of investments		0	0	0
Net Income		63,910	50,522	46,318
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		1,525,163	1,421,302	1,308,277
Capital expenditures		115,234	162,210	125,086
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		208,348	156,418	175,945
Depreciation and amortization		(12,852)	(12,049)	(11,320)
Operating Income (Loss)		25,133	19,674	19,528
Interest (expense) income, net		(4,315)	(4,370)	(4,237)
Income tax (provision) benefit		(4,922)	(4,805)	(4,753)
Equity earnings of investments		0	0	0
Net Income		15,511	14,167	14,088
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		485,345	444,702	408,001
Capital expenditures		34,071	36,906	36,193
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		41,544	41,082	40,715
Depreciation and amortization		(7,459)	(7,481)	(7,487)
Operating Income (Loss)		33,936	33,460	33,084
Interest (expense) income, net		(4,577)	(4,826)	(5,083)
Income tax (provision) benefit		(7,998)	(7,800)	(7,628)
Equity earnings of investments		0	0	0
Net Income		21,361	20,834	20,373
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		252,584	254,298	258,004
Capital expenditures		3,864	4,023	2,757
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0
Depreciation and amortization		0
Operating Income (Loss)		0	(1)	0
Interest (expense) income, net		0	0	0
Income tax (provision) benefit		(2,486)	(2,786)	(2,602)
Equity earnings of investments		9,339	10,221	9,547
Net Income		6,852	7,434	6,945
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	[1]	75,990	74,480	71,668
Capital expenditures		0	0	0
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0
Depreciation and amortization		0		0
Operating Income (Loss)		(768)	(983)	(882)
Interest (expense) income, net		41	121	1,235
Income tax (provision) benefit		619	198	236
Equity earnings of investments		(69)	0	0
Net Income		(1,873)	(539)	(850)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		467,954	495,483	443,278
Capital expenditures		0	0	0
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(64,150)	(53,324)	(56,896)
Depreciation and amortization		0
Operating Income (Loss)		0	0	0
Interest (expense) income, net		0	0	0
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]
Assets		(435,130)	(436,614)	(407,564)
Capital expenditures		0	0	0
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		556	765	806
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		22,728	12,157	16,070
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		40,866	40,402	40,020
Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0
Consolidation Elimination Entries [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues		606,584	538,633	568,855
Depreciation and amortization		(76,983)	(74,188)	(71,562)
Operating Income (Loss)		118,062	110,981	111,792
Interest (expense) income, net		(24,153)	(23,642)	(24,298)
Income tax (provision) benefit		(2,248)	(16,835)	(17,418)
Net Income		78,391	63,130	58,430
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		2,262,775	2,119,971	1,973,477
Capital expenditures		153,169	203,139	164,036
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		420,286	393,692	408,285
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		185,620	144,261	159,875
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		678	680	695
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		606,584	538,633	568,855
Depreciation and amortization		(76,983)	(74,188)	(71,562)
Operating Income (Loss)		118,062	110,981	111,792
Interest (expense) income, net		(24,153)	(23,642)	(24,298)
Income tax (provision) benefit		(2,248)	(16,835)	(17,418)
Net Income		78,391	63,130	58,430
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		420,842	394,457	409,091
Depreciation and amortization		(56,672)	(54,658)	(52,755)
Operating Income (Loss)		58,993	57,847	59,180
Interest (expense) income, net		(15,261)	(14,446)	(14,978)
Income tax (provision) benefit		10,672	(4,230)	(5,037)
Net Income		63,910	50,522	46,318
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		1,525,163	1,421,302	1,308,277
Capital expenditures		115,234	162,210	125,086
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		208,348	156,418	175,945
Depreciation and amortization		(12,852)	(12,049)	(11,320)
Operating Income (Loss)		25,133	19,674	19,528
Interest (expense) income, net		(4,315)	(4,370)	(4,237)
Income tax (provision) benefit		(4,922)	(4,805)	(4,753)
Net Income		15,511	14,167	14,088
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		485,345	444,702	408,001
Capital expenditures		34,071	36,906	36,193
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		41,544	41,082	40,715
Depreciation and amortization		(7,459)	(7,481)	(7,487)
Operating Income (Loss)		33,936	33,460	33,084
Interest (expense) income, net		(4,577)	(4,826)	(5,083)
Income tax (provision) benefit		(7,998)	(7,800)	(7,628)
Net Income		21,361	20,834	20,373
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		252,534	254,248	257,954
Capital expenditures		3,864	4,023	2,757
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(64,150)	(53,324)	(56,896)
Depreciation and amortization		0	0	0
Operating Income (Loss)		0	0	0
Interest (expense) income, net		0	0	0
Income tax (provision) benefit		0	0	0
Net Income		(22,391)	(22,393)	(22,349)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		(267)	(281)	(755)
Capital expenditures		0	0	0
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		556	765	806
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		22,728	12,157	16,070
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		$ 40,866	$ 40,402	$ 40,020

[1] The Transmission Investment segment represents MGE Energy's investment in equity method investees.