Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended									12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014		Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating revenues		$ 130,973	$ 140,795	$ 122,126	$ 170,134	$ 145,707		$ 135,135	$ 128,765	$ 210,245	$ 564,028	$ 619,852		$ 590,887
Depreciation and amortization											(44,225)	(40,695)		(38,838)
Other operating expenses											(395,548)	(441,059)		(424,062)
Operating Income (Loss)		22,178	46,177	24,049	31,851	29,566		40,120	24,441	43,971	124,255	138,098		127,987
Other (deductions) income, net											8,613	10,079		10,701
Interest (expense) income, net											(20,162)	(19,673)		(18,924)
Income before income taxes											112,706	128,504		119,764
Income tax (provision) benefit		(7,417)	(15,351)	(8,008)	(10,587)	(8,600)		(14,286)	(9,034)	(16,265)	(41,363)	(48,185)		(44,859)
Net Income		11,232	$ 28,354	$ 13,479	$ 18,278	15,186		$ 23,329	$ 14,087	$ 27,717	71,343	80,319		74,905
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		1,730,673				1,694,184	[1]				1,730,673	1,694,184	[1]	1,579,060
Capital expenditures											72,030	92,676		119,047
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues											412,528	394,849		403,957
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues											143,737	221,720		181,462
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues											7,763	3,283		5,468
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											564,028	619,852		590,887
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues											413,041	395,358		404,494
Depreciation and amortization											(29,945)	(26,933)		(25,780)
Other operating expenses											(318,001)	(297,409)		(316,277)
Operating Income (Loss)											65,095	71,016		62,437
Other (deductions) income, net											400	2,847		3,062
Interest (expense) income, net											(11,187)	(10,410)		(9,645)
Income before income taxes											54,308	63,453		55,854
Income tax (provision) benefit											(17,915)	(22,070)		(19,176)
Net Income											36,393	41,383		36,678
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		976,271				948,005	[1]				976,271	948,005	[1]	899,257
Capital expenditures											49,370	68,067		100,146
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues											155,517	230,086		194,091
Depreciation and amortization											(6,758)	(6,308)		(5,898)
Other operating expenses											(128,241)	(194,203)		(162,661)
Operating Income (Loss)											20,518	29,575		25,532
Other (deductions) income, net											(33)	(86)		59
Interest (expense) income, net											(3,203)	(3,229)		(2,986)
Income before income taxes											17,282	26,260		22,605
Income tax (provision) benefit											(6,915)	(10,480)		(9,168)
Net Income											10,367	15,780		13,437
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		299,792				307,582	[1]				299,792	307,582	[1]	265,694
Capital expenditures											18,787	22,104		15,554
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues											47,198	45,975		48,059
Depreciation and amortization											(7,475)	(7,407)		(7,156)
Other operating expenses											(158)	(139)		(128)
Operating Income (Loss)											39,565	38,429		40,775
Other (deductions) income, net											0	0		0
Interest (expense) income, net											(5,993)	(6,208)		(6,400)
Income before income taxes											33,572	32,221		34,375
Income tax (provision) benefit											(13,474)	(12,932)		(13,682)
Net Income											20,098	19,289		20,693
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		278,735				281,514	[1]				278,735	281,514	[1]	288,116
Capital expenditures											3,873	2,505		3,347
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											(19)	0		(1)
Operating Income (Loss)											(19)	0		(1)
Other (deductions) income, net											7,728	9,150		9,434
Interest (expense) income, net											0	0		0
Income before income taxes											7,709	9,150		9,433
Income tax (provision) benefit											(3,102)	(3,664)		(3,796)
Net Income											4,607	5,486		5,637
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		69,470				67,697	[1]				69,470	67,697	[1]	64,504
Capital expenditures											0	0		0
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues											0	0		0
Depreciation and amortization											(47)	(47)		(4)
Other operating expenses											(857)	(875)		(752)
Operating Income (Loss)											(904)	(922)		(756)
Other (deductions) income, net											518	(1,832)		(1,854)
Interest (expense) income, net											221	174		107
Income before income taxes											(165)	(2,580)		(2,503)
Income tax (provision) benefit											43	961		963
Net Income											(122)	(1,619)		(1,540)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		434,868				438,898	[1]				434,868	438,898	[1]	431,436
Capital expenditures											0	0		0
Operating Segments [Member] | Assets Not Allocated [Member]
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		49,753				41,124	[1]				49,753	41,124	[1]	19,853
Capital expenditures											0	0		0
Consolidation/Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues											(51,728)	(51,567)		(55,757)
Depreciation and amortization											0	0		0
Other operating expenses											51,728	51,567		55,757
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		(378,216)				(390,636)	[1]				(378,216)	(390,636)	[1]	(389,800)
Capital expenditures											0	0		0
Consolidation/Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues											513	509		537
Consolidation/Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues											11,780	8,366		12,629
Consolidation/Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues											39,435	42,692		42,591
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											564,065	619,895		590,925
Depreciation and amortization											(44,178)	(40,648)		(38,834)
Other operating expenses	[2]										(432,887)	(485,319)		(464,868)
Operating Income (Loss)	[2]										87,000	93,928		87,223
Other (deductions) income, net	[2]										4,848	7,857		8,253
Interest (expense) income, net											(20,383)	(19,847)		(19,031)
Income tax (provision) benefit											(41,406)	(49,145)		(45,822)
Net Income Including Noncontrolling Interest											71,465	81,938		76,445
Less Net Income Attributable to Noncontrolling Interest, net of tax											(26,097)	(26,310)		(27,438)
Net Income											45,368	55,628		49,007
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		1,673,784				1,639,351	[1]				1,673,784	1,639,351	[1]	1,530,643
Capital expenditures											72,030	92,676		119,047
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues											412,550	394,871		403,980
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues											143,752	221,741		181,477
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues											7,763	3,283		5,468
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues											0	0		0
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues											564,065	619,895		590,925
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues											413,041	395,358		404,494
Depreciation and amortization											(29,945)	(26,933)		(25,780)
Other operating expenses	[2]										(335,803)	(319,175)		(335,059)
Operating Income (Loss)	[2]										47,293	49,250		43,655
Other (deductions) income, net	[2]										287	2,543		2,668
Interest (expense) income, net											(11,187)	(10,410)		(9,645)
Net Income Including Noncontrolling Interest											36,393	41,383		36,678
Less Net Income Attributable to Noncontrolling Interest, net of tax											0	0		0
Net Income											36,393	41,383		36,678
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		976,271				948,005	[1]				976,271	948,005	[1]	899,257
Capital expenditures											49,370	68,067		100,146
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues											155,517	230,086		194,091
Depreciation and amortization											(6,758)	(6,308)		(5,898)
Other operating expenses	[2]										(135,124)	(204,597)		(171,717)
Operating Income (Loss)	[2]										13,635	19,181		16,476
Other (deductions) income, net	[2]										(65)	(172)		(53)
Interest (expense) income, net											(3,203)	(3,229)		(2,986)
Net Income Including Noncontrolling Interest											10,367	15,780		13,437
Less Net Income Attributable to Noncontrolling Interest, net of tax											0	0		0
Net Income											10,367	15,780		13,437
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		299,792				307,582	[1]				299,792	307,582	[1]	265,694
Capital expenditures											18,787	22,104		15,554
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues											47,198	45,975		48,059
Depreciation and amortization											(7,475)	(7,407)		(7,156)
Other operating expenses	[2]										(13,632)	(13,071)		(13,810)
Operating Income (Loss)	[2]										26,091	25,497		27,093
Other (deductions) income, net	[2]										0	0		0
Interest (expense) income, net											(5,993)	(6,208)		(6,400)
Net Income Including Noncontrolling Interest											20,098	19,289		20,693
Less Net Income Attributable to Noncontrolling Interest, net of tax											0	0		0
Net Income											20,098	19,289		20,693
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		278,685				281,464	[1]				278,685	281,464	[1]	288,066
Capital expenditures											3,873	2,505		3,347
MGE [Member] | 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	[2]										(19)	0		(1)
Operating Income (Loss)	[2]										(19)	0		(1)
Other (deductions) income, net	[2]										4,626	5,486		5,638
Interest (expense) income, net											0	0		0
Net Income Including Noncontrolling Interest											4,607	5,486		5,637
Less Net Income Attributable to Noncontrolling Interest, net of tax											0	0		0
Net Income											4,607	5,486		5,637
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		69,470				67,697	[1]				69,470	67,697	[1]	64,504
Capital expenditures											0	0		0
MGE [Member] | Operating Segments [Member] | Assets Not Allocated [Member]
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		49,753				41,124	[1]				49,753	41,124	[1]	19,853
Capital expenditures											0	0		0
MGE [Member] | Consolidation/Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues											(51,691)	(51,524)		(55,719)
Depreciation and amortization											0	0		0
Other operating expenses	[2]										51,691	51,524		55,719
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											(26,097)	(26,310)		(27,438)
Net Income											(26,097)	(26,310)		(27,438)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets		$ (187)				$ (6,521)	[1]				(187)	(6,521)	[1]	(6,731)
Capital expenditures											0	0		0
MGE [Member] | Consolidation/Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues											491	487		514
MGE [Member] | Consolidation/Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues											11,765	8,345		12,614
MGE [Member] | Consolidation/Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues											39,435	42,692		42,591
MGE [Member] | Consolidation/Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues											$ 0	$ 0		$ 0

[1] Reflects retrospective application of new accounting pronouncement. See Footnote 12 for additional information.

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