Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended										12 Months Ended
		Dec. 31, 2016		Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015		Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Segment Reporting Information [Line Items]
Operating revenues		$ 138,925		$ 136,717	$ 121,576	$ 147,527	$ 130,973		$ 140,795	$ 122,126	$ 170,134	$ 544,745		$ 564,028		$ 619,852
Depreciation and amortization												(44,646)		(44,225)		(40,695)
Other operating expenses												(371,871)		(395,548)		(441,059)
Operating Income (Loss)		23,958		46,527	28,212	29,531	22,178		46,177	24,049	31,851	128,228		124,255		138,098
Other (deductions) income, net												9,711		8,613		10,079
Interest (expense) income, net												(19,866)		(20,162)		(19,673)
Income before income taxes												118,073		112,706		128,504
Income tax (provision) benefit		(7,570)		(15,714)	(9,284)	(9,945)	(7,417)		(15,351)	(8,008)	(10,587)	(42,513)		(41,363)		(48,185)
Net Income		14,502		$ 27,880	$ 16,150	$ 17,028	11,232		$ 28,354	$ 13,479	$ 18,278	75,560		71,343		80,319
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		1,801,060					1,726,403	[1]				1,801,060		1,726,403	[1]	1,689,521	[1]
Capital expenditures												83,659		72,030		92,676
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues												409,006		412,528		394,849
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues												134,543		143,737		221,720
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues												1,196		7,763		3,283
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												544,745		564,028		619,852
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues												410,918		413,041		395,358
Depreciation and amortization												(29,122)		(29,945)		(26,933)
Other operating expenses												(310,941)		(318,001)		(297,409)
Operating Income (Loss)												70,855		65,095		71,016
Other (deductions) income, net												960		400		2,847
Interest (expense) income, net												(11,147)		(11,187)		(10,410)
Income before income taxes												60,668		54,308		63,453
Income tax (provision) benefit												(20,115)		(17,915)		(22,070)
Net Income												40,553		36,393		41,383
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		1,021,905					974,235	[1]				1,021,905		974,235	[1]	945,790	[1]
Capital expenditures												50,699		49,370		68,067
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues												155,921		155,517		230,086
Depreciation and amortization												(8,128)		(6,758)		(6,308)
Other operating expenses												(127,083)		(128,241)		(194,203)
Operating Income (Loss)												20,710		20,518		29,575
Other (deductions) income, net												30		(33)		(86)
Interest (expense) income, net												(3,223)		(3,203)		(3,229)
Income before income taxes												17,517		17,282		26,260
Income tax (provision) benefit												(6,894)		(6,915)		(10,480)
Net Income												10,623		10,367		15,780
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		318,603					298,435	[1]				318,603		298,435	[1]	306,106	[1]
Capital expenditures												29,136		18,787		22,104
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues												45,126		47,198		45,975
Depreciation and amortization												(7,372)		(7,475)		(7,407)
Other operating expenses												(155)		(158)		(139)
Operating Income (Loss)												37,599		39,565		38,429
Other (deductions) income, net												0		0		0
Interest (expense) income, net												(5,768)		(5,993)		(6,208)
Income before income taxes												31,831		33,572		32,221
Income tax (provision) benefit												(12,775)		(13,474)		(12,932)
Net Income												19,056		20,098		19,289
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		271,277					277,858	[1]				271,277		277,858	[1]	280,542	[1]
Capital expenditures												3,824		3,873		2,505
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues												0		0		0
Depreciation and amortization												0		0		0
Other operating expenses												(17)		(19)		0
Operating Income (Loss)												(17)		(19)		0
Other (deductions) income, net												8,429		7,728		9,150
Interest (expense) income, net												0		0		0
Income before income taxes												8,412		7,709		9,150
Income tax (provision) benefit												(2,836)		(3,102)		(3,664)
Net Income												5,576		4,607		5,486
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		74,535					69,470	[1]				74,535		69,470	[1]	67,697	[1]
Capital expenditures												0		0		0
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues												0		0		0
Depreciation and amortization												(24)		(47)		(47)
Other operating expenses												(895)		(857)		(875)
Operating Income (Loss)												(919)		(904)		(922)
Other (deductions) income, net												292		518		(1,832)
Interest (expense) income, net												272		221		174
Income before income taxes												(355)		(165)		(2,580)
Income tax (provision) benefit												107		43		961
Net Income												(248)		(122)		(1,619)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		465,202					434,868	[1]				465,202		434,868	[1]	438,898	[1]
Capital expenditures												0		0		0
Operating Segments [Member] | Assets Not Allocated [Member]
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		27,338					49,753	[1]				27,338		49,753	[1]	41,124	[1]
Capital expenditures												0		0		0
Consolidation/Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues												(67,220)		(51,728)		(51,567)
Depreciation and amortization												0		0		0
Other operating expenses												67,220		51,728		51,567
Operating Income (Loss)												0		0		0
Other (deductions) income, net												0		0		0
Interest (expense) income, net												0		0		0
Income before income taxes												0		0		0
Income tax (provision) benefit												0		0		0
Net Income												0		0		0
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		(377,800)					(378,216)	[1]				(377,800)		(378,216)	[1]	(390,636)	[1]
Capital expenditures												0		0		0
Consolidation/Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues												1,912		513		509
Consolidation/Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues												21,378		11,780		8,366
Consolidation/Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues												43,930		39,435		42,692
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												544,798		564,065		619,895
Depreciation and amortization												(44,622)		(44,178)		(40,648)
Other operating expenses	[2]											(410,627)		(432,887)		(485,319)
Operating Income (Loss)	[2]											89,549		87,000		93,928
Other (deductions) income, net	[2]											5,181		4,848		7,857
Interest (expense) income, net												(20,138)		(20,383)		(19,847)
Income tax (provision) benefit												(41,791)		(41,406)		(49,145)
Net Income Including Noncontrolling Interest												74,592		71,465		81,938
Less Net Income Attributable to Noncontrolling Interest, net of tax												(23,358)		(26,097)		(26,310)
Net Income												51,234		45,368		55,628
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		1,638,852					1,669,514	[1]				1,638,852		1,669,514	[1]	1,634,688	[1]
Capital expenditures												83,659		72,030		92,676
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues												409,030		412,550		394,871
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues												134,572		143,752		221,741
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues												1,196		7,763		3,283
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues												0	[3]	0		0
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues												544,798		564,065		619,895
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues												410,918		413,041		395,358
Depreciation and amortization												(29,122)		(29,945)		(26,933)
Other operating expenses	[2]											(330,924)		(335,803)		(319,175)
Operating Income (Loss)	[2]											50,872		47,293		49,250
Other (deductions) income, net	[2]											828		287		2,543
Interest (expense) income, net												(11,147)		(11,187)		(10,410)
Net Income Including Noncontrolling Interest												40,553		36,393		41,383
Less Net Income Attributable to Noncontrolling Interest, net of tax												0		0		0
Net Income												40,553		36,393		41,383
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		1,021,905					974,235	[1]				1,021,905		974,235	[1]	945,790	[1]
Capital expenditures												50,699		49,370		68,067
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues												155,921		155,517		230,086
Depreciation and amortization												(8,128)		(6,758)		(6,308)
Other operating expenses	[2]											(133,940)		(135,124)		(204,597)
Operating Income (Loss)	[2]											13,853		13,635		19,181
Other (deductions) income, net	[2]											(7)		(65)		(172)
Interest (expense) income, net												(3,223)		(3,203)		(3,229)
Net Income Including Noncontrolling Interest												10,623		10,367		15,780
Less Net Income Attributable to Noncontrolling Interest, net of tax												0		0		0
Net Income												10,623		10,367		15,780
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		318,603					298,435	[1]				318,603		298,435	[1]	306,106	[1]
Capital expenditures												29,136		18,787		22,104
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues												45,126		47,198		45,975
Depreciation and amortization												(7,372)		(7,475)		(7,407)
Other operating expenses	[2]											(12,930)		(13,632)		(13,071)
Operating Income (Loss)	[2]											24,824		26,091		25,497
Other (deductions) income, net	[2]											0		0		0
Interest (expense) income, net												(5,768)		(5,993)		(6,208)
Net Income Including Noncontrolling Interest												19,056		20,098		19,289
Less Net Income Attributable to Noncontrolling Interest, net of tax												0		0		0
Net Income												19,056		20,098		19,289
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		271,227					277,808	[1]				271,227		277,808	[1]	280,492	[1]
Capital expenditures												3,824		3,873		2,505
MGE [Member] | Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues												0	[3]	0		0
Depreciation and amortization												0	[3]	0		0
Other operating expenses	[2]											0	[3]	(19)		0
Operating Income (Loss)	[2]											0	[3]	(19)		0
Other (deductions) income, net	[2]											4,360	[3]	4,626		5,486
Interest (expense) income, net												0	[3]	0		0
Net Income Including Noncontrolling Interest												4,360	[3]	4,607		5,486
Less Net Income Attributable to Noncontrolling Interest, net of tax												0	[3]	0		0
Net Income												4,360	[3]	4,607		5,486
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		0	[4]				69,470	[1]				0	[4]	69,470	[1]	67,697	[1]
Capital expenditures												0		0		0
MGE [Member] | Operating Segments [Member] | Assets Not Allocated [Member]
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		27,338					49,753	[1]				27,338		49,753	[1]	41,124	[1]
Capital expenditures												0		0		0
MGE [Member] | Consolidation/Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues												(67,167)		(51,691)		(51,524)
Depreciation and amortization												0		0		0
Other operating expenses	[2]											67,167		51,691		51,524
Operating Income (Loss)	[2]											0		0		0
Other (deductions) income, net	[2]											0		0		0
Interest (expense) income, net												0		0		0
Net Income Including Noncontrolling Interest												0		0		0
Less Net Income Attributable to Noncontrolling Interest, net of tax												(23,358)		(26,097)		(26,310)
Net Income												(23,358)		(26,097)		(26,310)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		$ (221)					$ (187)	[1]				(221)		(187)	[1]	(6,521)	[1]
Capital expenditures												0		0		0
MGE [Member] | Consolidation/Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues												1,888		491		487
MGE [Member] | Consolidation/Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues												21,349		11,765		8,345
MGE [Member] | Consolidation/Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues												43,930		39,435		42,692
MGE [Member] | Consolidation/Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues												$ 0	[3]	$ 0		$ 0

[1] Reflects retrospective application of new accounting pronouncement. See Footnote 19 for additional information.

[2] Amounts are shown net of the related tax expense, consistent with the presentation on the MGE Consolidated Statements of Income.

[3] As of July 31, 2016, MGE no longer consolidates MGE Energy's proportionate share of equity earnings in MGE Transco. See Footnote 4 for additional information.

[4] In December 2016, MGE’s ownership interest in MGE Transco was transferred to MGE Energy, see Footnote 4 for additional information.