Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended				12 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013		Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating revenues	$ 128,765		$ 128,288		$ 339,010		$ 295,525
Depreciation and amortization	(10,069)		(9,530)		(19,815)		(19,154)
Other operating expenses	(94,255)		(94,261)		(250,783)		(214,246)
Operating Income	24,441		24,497		68,412		62,125
Other income (deductions), net	3,548		2,711		8,100		6,020
Interest (expense) income, net	(4,868)		(4,657)		(9,409)		(9,332)
Income before income taxes	23,121		22,551		67,103		58,813
Income tax (provision) benefit	(9,034)		(8,660)		(25,299)		(22,338)
Net Income (Loss)	14,087		13,891		41,804		36,475
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,596,963				1,596,963				1,579,060
Capital expenditures					42,272		63,137		119,047
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	96,697		96,846		195,549		190,340
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	31,218		30,042		141,931		102,509
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	850		1,400		1,530		2,676
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	128,765		128,288		339,010		295,525
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	96,824		96,975		195,794		190,578
Depreciation and amortization	(6,641)		(6,314)		(12,978)		(12,714)
Other operating expenses	(76,812)		(78,051)		(154,713)		(152,976)
Operating Income	13,371		12,610		28,103		24,888
Other income (deductions), net	1,036		485		2,863		1,060
Interest (expense) income, net	(2,534)		(2,315)		(4,739)		(4,719)
Income before income taxes	11,873		10,780		26,227		21,229
Income tax (provision) benefit	(4,491)		(3,694)		(8,844)		(7,127)
Net Income (Loss)	7,382		7,086		17,383		14,102
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	915,507				915,507				899,257
Capital expenditures					34,133				100,146
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	33,110		32,858		147,447		110,201
Depreciation and amortization	(1,562)		(1,435)		(3,125)		(2,860)
Other operating expenses	(29,865)		(29,572)		(122,708)		(90,009)
Operating Income	1,683		1,851		21,614		17,332
Other income (deductions), net	(17)		(185)		(52)		(23)
Interest (expense) income, net	(817)		(759)		(1,621)		(1,437)
Income before income taxes	849		907		19,941		15,872
Income tax (provision) benefit	(364)		(606)		(8,029)		(6,595)
Net Income (Loss)	485		301		11,912		9,277
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	247,229				247,229				265,694
Capital expenditures					7,289				15,554
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	11,523		12,091		22,873		23,940
Depreciation and amortization	(1,855)		(1,781)		(3,689)		(3,580)
Other operating expenses	(30)		(26)		(70)		(63)
Operating Income	9,638		10,284		19,114		20,297
Other income (deductions), net	0		0		0		0
Interest (expense) income, net	(1,559)		(1,605)		(3,131)		(3,218)
Income before income taxes	8,079		8,679		15,983		17,079
Income tax (provision) benefit	(3,242)		(3,483)		(6,414)		(6,740)
Net Income (Loss)	4,837		5,196		9,569		10,339
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	286,855				286,855				288,116
Capital expenditures					850				3,347
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0		0		0
Depreciation and amortization	0		0		0		0
Other operating expenses	0		0		0		0
Operating Income	0		0		0		0
Other income (deductions), net	2,402		2,309		4,883		4,705
Interest (expense) income, net	0		0		0		0
Income before income taxes	2,402		2,309		4,883		4,705
Income tax (provision) benefit	(963)		(927)		(1,961)		(1,898)
Net Income (Loss)	1,439		1,382		2,922		2,807
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	66,617				66,617				64,504
Capital expenditures					0				0
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0		0		0
Depreciation and amortization	(11)		0		(23)		0
Other operating expenses	(240)		(248)		(396)		(392)
Operating Income	(251)		(248)		(419)		(392)
Other income (deductions), net	127		102		406		278
Interest (expense) income, net	42		22		82		42
Income before income taxes	(82)		(124)		69		(72)
Income tax (provision) benefit	26		50		(51)		22
Net Income (Loss)	(56)		(74)		18		(50)
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	438,134				438,134				431,436
Capital expenditures					0				0
Operating Segments [Member] | Assets Not Allocated [Member]
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	31,187				31,187				19,853
Capital expenditures					0				0
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(12,692)		(13,636)		(27,104)		(29,194)
Depreciation and amortization	0		0		0		0
Other operating expenses	12,692		13,636		27,104		29,194
Operating Income	0		0		0		0
Other income (deductions), net	0		0		0		0
Interest (expense) income, net	0		0		0		0
Income before income taxes	0		0		0		0
Income tax (provision) benefit	0		0		0		0
Net Income (Loss)	0		0		0		0
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	(388,566)				(388,566)				(389,800)
Capital expenditures					0				0
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	127		129		245		238
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,892		2,816		5,516		7,692
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,673		10,691		21,343		21,264
Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0		0		0
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	128,775		128,288		339,031		295,525
Depreciation and amortization	(10,058)		(9,530)		(19,792)		(19,154)
Other operating expenses	(101,943)	[1]	(101,582)	[1]	(273,250)	[1]	(234,292)	[1]
Operating Income	16,774	[1]	17,176	[1]	45,989	[1]	42,079	[1]
Other income (deductions), net	2,279	[1]	1,468	[1]	5,288	[1]	3,820	[1]
Interest (expense) income, net	(4,910)		(4,679)		(9,491)		(9,374)
Income tax (provision) benefit	(7,918)		(7,569)		(22,842)		(20,439)
Net Income Including Noncontrolling Interest	14,143		13,965		41,786		36,525
Less Net Income Attributable to Noncontrolling Interest, net of tax	(6,621)		(6,860)		(13,131)		(13,686)
Net Income (Loss)	7,522		7,105		28,655		22,839
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,540,589				1,540,589				1,530,643
Capital expenditures					42,272		63,137		119,047
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	96,702		96,846		195,560		190,340
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	31,223		30,042		141,941		102,509
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	850		1,400		1,530		2,676
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0		0		0
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	128,775		128,288		339,031		295,525
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	96,824		96,975		195,794		190,578
Depreciation and amortization	(6,641)		(6,314)		(12,978)		(12,714)
Other operating expenses	(81,165)	[1]	(81,579)	[1]	(163,211)	[1]	(160,085)	[1]
Operating Income	9,018	[1]	9,082	[1]	19,605	[1]	17,779	[1]
Other income (deductions), net	898	[1]	319	[1]	2,517	[1]	1,042	[1]
Interest (expense) income, net	(2,534)		(2,315)		(4,739)		(4,719)
Net Income Including Noncontrolling Interest	7,382		7,086		17,383		14,102
Less Net Income Attributable to Noncontrolling Interest, net of tax	0		0		0		0
Net Income (Loss)	7,382		7,086		17,383		14,102
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	915,507				915,507				899,257
Capital expenditures					34,133				100,146
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	33,110		32,858		147,447		110,201
Depreciation and amortization	(1,562)		(1,435)		(3,125)		(2,860)
Other operating expenses	(30,188)	[1]	(30,130)	[1]	(130,638)	[1]	(96,598)	[1]
Operating Income	1,360	[1]	1,293	[1]	13,684	[1]	10,743	[1]
Other income (deductions), net	(58)	[1]	(233)	[1]	(151)	[1]	(29)	[1]
Interest (expense) income, net	(817)		(759)		(1,621)		(1,437)
Net Income Including Noncontrolling Interest	485		301		11,912		9,277
Less Net Income Attributable to Noncontrolling Interest, net of tax	0		0		0		0
Net Income (Loss)	485		301		11,912		9,277
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	247,229				247,229				265,694
Capital expenditures					7,289				15,554
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	11,523		12,091		22,873		23,940
Depreciation and amortization	(1,855)		(1,781)		(3,689)		(3,580)
Other operating expenses	(3,272)	[1]	(3,509)	[1]	(6,484)	[1]	(6,803)	[1]
Operating Income	6,396	[1]	6,801	[1]	12,700	[1]	13,557	[1]
Other income (deductions), net	0	[1]	0	[1]	0	[1]	0	[1]
Interest (expense) income, net	(1,559)		(1,605)		(3,131)		(3,218)
Net Income Including Noncontrolling Interest	4,837		5,196		9,569		10,339
Less Net Income Attributable to Noncontrolling Interest, net of tax	0		0		0		0
Net Income (Loss)	4,837		5,196		9,569		10,339
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	286,805				286,805				288,066
Capital expenditures					850				3,347
MGE [Member] | Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0		0		0
Depreciation and amortization	0		0		0		0
Other operating expenses	0	[1]	0	[1]	0	[1]	0	[1]
Operating Income	0	[1]	0	[1]	0	[1]	0	[1]
Other income (deductions), net	1,439	[1]	1,382	[1]	2,922	[1]	2,807	[1]
Interest (expense) income, net	0		0		0		0
Net Income Including Noncontrolling Interest	1,439		1,382		2,922		2,807
Less Net Income Attributable to Noncontrolling Interest, net of tax	0		0		0		0
Net Income (Loss)	1,439		1,382		2,922		2,807
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	66,617				66,617				64,504
Capital expenditures					0				0
MGE [Member] | Operating Segments [Member] | Assets Not Allocated [Member]
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	31,187				31,187				19,853
Capital expenditures					0				0
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(12,682)		(13,636)		(27,083)		(29,194)
Depreciation and amortization	0		0		0		0
Other operating expenses	12,682	[1]	13,636	[1]	27,083	[1]	29,194	[1]
Operating Income	0	[1]	0	[1]	0	[1]	0	[1]
Other income (deductions), net	0	[1]	0	[1]	0	[1]	0	[1]
Interest (expense) income, net	0		0		0		0
Net Income Including Noncontrolling Interest	0		0		0		0
Less Net Income Attributable to Noncontrolling Interest, net of tax	(6,621)		(6,860)		(13,131)		(13,686)
Net Income (Loss)	(6,621)		(6,860)		(13,131)		(13,686)
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	(6,756)				(6,756)				(6,731)
Capital expenditures					0				0
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	122		129		234		238
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,887		2,816		5,506		7,692
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,673		10,691		21,343		21,264
MGE [Member] | Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 0		$ 0		$ 0		$ 0

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