Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Segment Reporting Information [Line Items]
Operating revenues	$ 155,263	$ 140,099	$ 128,288	$ 167,237	$ 137,005	$ 137,838	$ 117,221	$ 149,259	$ 590,887		$ 541,323		$ 546,382
Depreciation and amortization									(38,838)		(38,707)		(40,942)
Other operating expenses									(424,062)		(389,853)		(397,572)
Operating Income	25,962	39,900	24,497	37,628	19,350	39,888	25,081	28,444	127,987		112,763		107,868
Other (deductions) income, net									10,701		10,069		9,214
Interest (expense) income, net									(18,924)		(19,467)		(20,162)
Income before income taxes									119,764		103,365		96,920
Income tax (provision) benefit	(7,829)	(14,692)	(8,660)	(13,678)	(6,208)	(14,253)	(8,596)	(9,862)	(44,859)		(38,919)		(35,992)
Net Income	14,077	24,353	13,891	22,584	10,486	23,642	14,270	16,048	74,905		64,446		60,928
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	1,579,060				1,586,924				1,579,060		1,586,924		1,458,882
Capital expenditures									119,047		98,435		65,176
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									404,494		392,852		376,353
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues									194,091		152,541		177,711
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues									48,059		43,945		43,401
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] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									403,957		392,365		375,858
Depreciation and amortization									(25,780)		(26,031)		(28,323)
Other operating expenses									(316,277)		(300,149)		(292,080)
Operating Income									62,437		66,672		55,950
Other (deductions) income, net									3,062		1,145		71
Interest (expense) income, net									(9,645)		(10,189)		(10,849)
Income before income taxes									55,854		57,628		45,172
Income tax (provision) benefit									(19,176)		(20,906)		(15,334)
Net Income									36,678		36,722		29,838
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	899,257				888,444				899,257		888,444		794,738
Capital expenditures									100,146		81,965		47,206
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues									181,462		139,727		165,271
Depreciation and amortization									(5,898)		(5,569)		(5,593)
Other operating expenses									(162,661)		(136,567)		(155,444)
Operating Income									25,532		10,405		16,674
Other (deductions) income, net									59		323		20
Interest (expense) income, net									(2,986)		(2,874)		(3,060)
Income before income taxes									22,605		7,854		13,634
Income tax (provision) benefit									(9,168)		(2,769)		(5,249)
Net Income									13,437		5,085		8,385
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	265,694				285,468				265,694		285,468		285,702
Capital expenditures									15,554		13,812		15,830
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues									5,468		9,231		5,253
Depreciation and amortization									(7,156)		(7,107)		(7,026)
Other operating expenses									(128)		(121)		(174)
Operating Income									40,775		36,717		36,201
Other (deductions) income, net									0		0		0
Interest (expense) income, net									(6,400)		(6,537)		(6,331)
Income before income taxes									34,375		30,180		29,870
Income tax (provision) benefit									(13,682)		(12,113)		(11,988)
Net Income									20,693		18,067		17,882
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	288,116				323,216				288,116		323,216		299,421
Capital expenditures									3,347		2,658		2,140
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									(1)		0		0
Operating Income									(1)		0		0
Other (deductions) income, net									9,434		9,080		8,614
Interest (expense) income, net									0		0		0
Income before income taxes									9,433		9,080		8,614
Income tax (provision) benefit									(3,796)		(3,648)		(3,467)
Net Income									5,637		5,432		5,147
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	64,504				61,064				64,504		61,064		57,006
Capital expenditures									0		0		0
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues									0		0		0
Depreciation and amortization									(4)		0		0
Other operating expenses									(752)		(1,031)		(957)
Operating Income									(756)		(1,031)		(957)
Other (deductions) income, net									(1,854)		(479)		509
Interest (expense) income, net									107		133		78
Income before income taxes									(2,503)		(1,377)		(370)
Income tax (provision) benefit									963		517		46
Net Income									(1,540)		(860)		(324)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	431,436				413,291				431,436		413,291		401,862
Capital expenditures									0		0		0
Operating Segments [Member] | Assets Not Allocated [Member]
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	19,853				18,559				19,853		18,559		32,882
Capital expenditures									0		0		0
Consolidation/Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues									(55,757)		(48,015)		(51,083)
Depreciation and amortization									0		0		0
Other operating expenses									55,757		48,015		51,083
Operating Income									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	(389,800)				(403,118)				(389,800)		(403,118)		(412,729)
Capital expenditures									0		0		0
Consolidation/Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									537		487		495
Consolidation/Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues									12,629		12,814		12,440
Consolidation/Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues									42,591		34,714		38,148
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									590,925		541,323		546,382
Depreciation and amortization									(38,834)		(38,707)		(40,942)
Other operating expenses									(464,868)	[1]	(424,156)	[1]	(428,903)	[1]
Operating Income									87,223	[1]	78,460	[1]	76,537	[1]
Other (deductions) income, net									8,253	[1]	6,446	[1]	4,955	[1]
Interest (expense) income, net									(19,031)		(19,600)		(20,240)
Income tax (provision) benefit									(45,822)		(39,435)		(36,039)
Net Income Including Noncontrolling Interest									76,445		65,306		61,252
Less Net Income Attributable to Noncontrolling Interest, net of tax									(27,438)		(24,489)		(23,970)
Net Income									49,007		40,817		37,282
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	1,530,643				1,553,651				1,530,643		1,553,651		1,433,793
Capital expenditures									119,047		98,435		65,176
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									404,494		392,852		376,353
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues									194,091		152,541		177,711
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues									48,059		43,945		43,401
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues									0		0		0
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									403,980		392,365		375,858
Depreciation and amortization									(25,780)		(26,031)		(28,323)
Other operating expenses									(335,059)	[1]	(320,701)	[1]	(307,193)	[1]
Operating Income									43,655	[1]	46,120	[1]	40,837	[1]
Other (deductions) income, net									2,668	[1]	791	[1]	(150)	[1]
Interest (expense) income, net									(9,645)		(10,189)		(10,849)
Net Income Including Noncontrolling Interest									36,678		36,722		29,838
Less Net Income Attributable to Noncontrolling Interest, net of tax									0		0		0
Net Income									36,678		36,722		29,838
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	899,257				888,444				899,257		888,444		794,738
Capital expenditures									100,146		81,965		47,206
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues									181,477		139,727		165,271
Depreciation and amortization									(5,898)		(5,569)		(5,593)
Other operating expenses									(171,717)	[1]	(139,236)	[1]	(160,631)	[1]
Operating Income									16,476	[1]	7,736	[1]	11,487	[1]
Other (deductions) income, net									(53)	[1]	223	[1]	(42)	[1]
Interest (expense) income, net									(2,986)		(2,874)		(3,060)
Net Income Including Noncontrolling Interest									13,437		5,085		8,385
Less Net Income Attributable to Noncontrolling Interest, net of tax									0		0		0
Net Income									13,437		5,085		8,385
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	265,694				285,468				265,694		285,468		285,702
Capital expenditures									15,554		13,812		15,830
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues									5,468		9,231		5,253
Depreciation and amortization									(7,156)		(7,107)		(7,026)
Other operating expenses									(13,810)	[1]	(12,234)	[1]	(12,162)	[1]
Operating Income									27,093	[1]	24,604	[1]	24,213	[1]
Other (deductions) income, net									0	[1]	0	[1]	0	[1]
Interest (expense) income, net									(6,400)		(6,537)		(6,331)
Net Income Including Noncontrolling Interest									20,693		18,067		17,882
Less Net Income Attributable to Noncontrolling Interest, net of tax									0		0		0
Net Income									20,693		18,067		17,882
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	288,066				323,166				288,066		323,166		299,171
Capital expenditures									3,347		2,658		2,140
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									(1)	[1]	0	[1]	0	[1]
Operating Income									(1)	[1]	0	[1]	0	[1]
Other (deductions) income, net									5,638	[1]	5,432	[1]	5,147	[1]
Interest (expense) income, net									0		0		0
Net Income Including Noncontrolling Interest									5,637		5,432		5,147
Less Net Income Attributable to Noncontrolling Interest, net of tax									0		0		0
Net Income									5,637		5,432		5,147
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	64,504				61,064				64,504		61,064		57,006
Capital expenditures									0		0		0
MGE [Member] | Operating Segments [Member] | Assets Not Allocated [Member]
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	19,853				18,559				19,853		18,559		32,882
Capital expenditures									0		0		0
MGE [Member] | Consolidation/Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues									(55,719)		(48,015)		(51,083)
Depreciation and amortization									0		0		0
Other operating expenses									55,719	[1]	48,015	[1]	51,083	[1]
Operating Income									0	[1]	0	[1]	0	[1]
Other (deductions) income, net									0	[1]	0	[1]	0	[1]
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									(27,438)		(24,489)		(23,970)
Net Income									(27,438)		(24,489)		(23,970)
Segment Reporting Information Assets And Capital Expenditures [Abstract]
Assets	(6,731)				(23,050)				(6,731)		(23,050)		(35,706)
Capital expenditures									0		0		0
MGE [Member] | Consolidation/Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues									514		487		495
MGE [Member] | Consolidation/Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues									12,614		12,814		12,440
MGE [Member] | Consolidation/Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues									42,591		34,714		38,148
MGE [Member] | Consolidation/Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues									$ 0		$ 0		$ 0

[1] *Amounts are shown net of the related tax expense, consistent with the presentation on the consolidated MGE Income Statement.