Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				12 Months Ended
	Mar. 31, 2014		Mar. 31, 2013		Dec. 31, 2013
Segment Reporting Information [Line Items]
Operating revenues	$ 210,245		$ 167,237
Depreciation and amortization	(9,746)		(9,624)
Other operating expenses	(156,528)		(119,985)
Operating Income	43,971		37,628
Other income (deductions), net	4,552		3,309
Interest (expense) income, net	(4,541)		(4,675)
Income before income taxes	43,982		36,262
Income tax (provision) benefit	(16,265)		(13,678)
Net Income (Loss)	27,717		22,584
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,610,423				1,579,060
Capital expenditures	21,800		29,164		119,047
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	98,852		93,494
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	110,713		72,467
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	680		1,276
Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0
All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	98,970		93,603
Depreciation and amortization	(6,337)		(6,400)
Other operating expenses	(77,901)		(74,925)
Operating Income	14,732		12,278
Other income (deductions), net	1,827		575
Interest (expense) income, net	(2,205)		(2,404)
Income before income taxes	14,354		10,449
Income tax (provision) benefit	(4,353)		(3,433)
Net Income (Loss)	10,001		7,016
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	905,319				899,257
Capital expenditures	18,906				100,146
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	114,337		77,343
Depreciation and amortization	(1,563)		(1,425)
Other operating expenses	(92,843)		(60,437)
Operating Income	19,931		15,481
Other income (deductions), net	(35)		162
Interest (expense) income, net	(804)		(678)
Income before income taxes	19,092		14,965
Income tax (provision) benefit	(7,665)		(5,989)
Net Income (Loss)	11,427		8,976
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	268,294				265,694
Capital expenditures	2,384				15,554
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	11,350		11,849
Depreciation and amortization	(1,834)		(1,799)
Other operating expenses	(40)		(37)
Operating Income	9,476		10,013
Other income (deductions), net	0		0
Interest (expense) income, net	(1,572)		(1,613)
Income before income taxes	7,904		8,400
Income tax (provision) benefit	(3,172)		(3,257)
Net Income (Loss)	4,732		5,143
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	312,223				288,116
Capital expenditures	510				3,347
Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0
Depreciation and amortization	0		0
Other operating expenses	0		0
Operating Income	0		0
Other income (deductions), net	2,481		2,396
Interest (expense) income, net	0		0
Income before income taxes	2,481		2,396
Income tax (provision) benefit	(998)		(971)
Net Income (Loss)	1,483		1,425
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	65,600				64,504
Capital expenditures	0				0
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0
Depreciation and amortization	(12)		0
Other operating expenses	(156)		(144)
Operating Income	(168)		(144)
Other income (deductions), net	279		176
Interest (expense) income, net	40		20
Income before income taxes	151		52
Income tax (provision) benefit	(77)		(28)
Net Income (Loss)	74		24
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	432,919				431,436
Capital expenditures	0				0
Operating Segments [Member] | Assets Not Allocated [Member]
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	40,011				19,853
Capital expenditures	0				0
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(14,412)		(15,558)
Depreciation and amortization	0		0
Other operating expenses	14,412		15,558
Operating Income	0		0
Other income (deductions), net	0		0
Interest (expense) income, net	0		0
Income before income taxes	0		0
Income tax (provision) benefit	0		0
Net Income (Loss)	0		0
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	(413,943)				(389,800)
Capital expenditures	0				0
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	118		109
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,624		4,876
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,670		10,573
Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0
Consolidation Elimination Entries [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues	210,256		167,237
Depreciation and amortization	(9,734)		(9,624)
Other operating expenses	(171,307)	[1]	(132,710)	[1]
Operating Income	29,215	[1]	24,903	[1]
Other income (deductions), net	3,009	[1]	2,352	[1]
Interest (expense) income, net	(4,581)		(4,695)
Income tax (provision) benefit	(14,924)		(12,870)
Net Income Including Noncontrolling Interest	27,643		22,560
Less Net Income Attributable to Noncontrolling Interest, net of tax	(6,510)		(6,826)
Net Income (Loss)	21,133		15,734
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,555,393				1,530,643
Capital expenditures	21,800		29,164		119,047
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	98,858		93,494
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	110,718		72,467
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	680		1,276
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	98,970		93,603
Depreciation and amortization	(6,337)		(6,400)
Other operating expenses	(82,046)	[1]	(78,506)	[1]
Operating Income	10,587	[1]	8,697	[1]
Other income (deductions), net	1,619	[1]	723	[1]
Interest (expense) income, net	(2,205)		(2,404)
Net Income Including Noncontrolling Interest	10,001		7,016
Less Net Income Attributable to Noncontrolling Interest, net of tax	0		0
Net Income (Loss)	10,001		7,016
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	907,952				899,257
Capital expenditures	18,906				100,146
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	114,337		77,343
Depreciation and amortization	(1,563)		(1,425)
Other operating expenses	(100,450)	[1]	(66,468)	[1]
Operating Income	12,324	[1]	9,450	[1]
Other income (deductions), net	(93)	[1]	204	[1]
Interest (expense) income, net	(804)		(678)
Net Income Including Noncontrolling Interest	11,427		8,976
Less Net Income Attributable to Noncontrolling Interest, net of tax	0		0
Net Income (Loss)	11,427		8,976
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	266,383				265,694
Capital expenditures	2,384				15,554
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	11,350		11,849
Depreciation and amortization	(1,834)		(1,799)
Other operating expenses	(3,212)	[1]	(3,294)	[1]
Operating Income	6,304	[1]	6,756	[1]
Other income (deductions), net	0	[1]	0	[1]
Interest (expense) income, net	(1,572)		(1,613)
Net Income Including Noncontrolling Interest	4,732		5,143
Less Net Income Attributable to Noncontrolling Interest, net of tax	0		0
Net Income (Loss)	4,732		5,143
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	288,268				288,066
Capital expenditures	510				3,347
MGE [Member] | Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0
Depreciation and amortization	0		0
Other operating expenses	0	[1]	0	[1]
Operating Income	0	[1]	0	[1]
Other income (deductions), net	1,483	[1]	1,425	[1]
Interest (expense) income, net	0		0
Net Income Including Noncontrolling Interest	1,483		1,425
Less Net Income Attributable to Noncontrolling Interest, net of tax	0		0
Net Income (Loss)	1,483		1,425
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	65,600				64,504
Capital expenditures	0				0
MGE [Member] | Operating Segments [Member] | Assets Not Allocated [Member]
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	39,883				19,853
Capital expenditures	0				0
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(14,401)		(15,558)
Depreciation and amortization	0		0
Other operating expenses	14,401	[1]	15,558	[1]
Operating Income	0	[1]	0	[1]
Other income (deductions), net	0	[1]	0	[1]
Interest (expense) income, net	0		0
Net Income Including Noncontrolling Interest	0		0
Less Net Income Attributable to Noncontrolling Interest, net of tax	(6,510)		(6,826)
Net Income (Loss)	(6,510)		(6,826)
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	(12,693)				(6,731)
Capital expenditures	0				0
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	112		109
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	3,619		4,876
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,670		10,573
MGE [Member] | Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 0		$ 0

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