Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Segment Reporting Information [Line Items]
Operating revenues	$ 170,134		$ 210,245
Depreciation and amortization	(10,849)		(9,746)
Other operating expenses	(127,434)		(156,528)
Operating Income	31,851		43,971
Other income (deductions), net	2,105		4,552
Interest (expense) income, net	(5,091)		(4,541)
Income before income taxes	28,865		43,982
Income tax (provision) benefit	(10,587)		(16,265)
Net Income (Loss)	18,278		27,717
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	98,240		98,852
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	69,928		110,713
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,966		680
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]
Segment Reporting Information [Line Items]
Operating revenues	170,134		210,245
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	98,355		98,970
Depreciation and amortization	(7,332)		(6,337)
Other operating expenses	(79,800)		(77,901)
Operating Income	11,223		14,732
Other income (deductions), net	90		1,827
Interest (expense) income, net	(2,819)		(2,205)
Income before income taxes	8,494		14,354
Income tax (provision) benefit	(2,383)		(4,353)
Net Income (Loss)	6,111		10,001
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	72,653		114,337
Depreciation and amortization	(1,642)		(1,563)
Other operating expenses	(60,068)		(92,843)
Operating Income	10,943		19,931
Other income (deductions), net	(1)		(35)
Interest (expense) income, net	(804)		(804)
Income before income taxes	10,138		19,092
Income tax (provision) benefit	(4,081)		(7,665)
Net Income (Loss)	6,057		11,427
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	11,813		11,350
Depreciation and amortization	(1,863)		(1,834)
Other operating expenses	(50)		(40)
Operating Income	9,900		9,476
Other income (deductions), net	0		0
Interest (expense) income, net	(1,518)		(1,572)
Income before income taxes	8,382		7,904
Income tax (provision) benefit	(3,364)		(3,172)
Net Income (Loss)	5,018		4,732
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	1,881		2,481
Interest (expense) income, net	0		0
Income before income taxes	1,881		2,481
Income tax (provision) benefit	(756)		(998)
Net Income (Loss)	1,125		1,483
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0
Depreciation and amortization	(12)		(12)
Other operating expenses	(203)		(156)
Operating Income	(215)		(168)
Other income (deductions), net	135		279
Interest (expense) income, net	50		40
Income before income taxes	(30)		151
Income tax (provision) benefit	(3)		(77)
Net Income (Loss)	(33)		74
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(12,687)		(14,412)
Depreciation and amortization	0		0
Other operating expenses	12,687		14,412
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
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	115		118
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,725		3,624
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	9,847		10,670
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	170,144		210,256
Depreciation and amortization	(10,837)		(9,734)
Other operating expenses	(137,017)	[1]	(171,307)	[1]
Operating Income	22,290	[1]	29,215	[1]
Other income (deductions), net	1,162	[1]	3,009	[1]
Interest (expense) income, net	(5,141)		(4,581)
Income tax (provision) benefit	(9,776)		(14,924)
Net Income Including Noncontrolling Interest	18,311		27,643
Less Net Income Attributable to Noncontrolling Interest, net of tax	(6,553)		(6,510)
Net Income (Loss)	11,758		21,133
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	98,245		98,858
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	69,933		110,718
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,966		680
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0		0
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	170,144		210,256
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	98,355		98,970
Depreciation and amortization	(7,332)		(6,337)
Other operating expenses	(82,142)	[1]	(82,046)	[1]
Operating Income	8,881	[1]	10,587	[1]
Other income (deductions), net	49	[1]	1,619	[1]
Interest (expense) income, net	(2,819)		(2,205)
Net Income Including Noncontrolling Interest	6,111		10,001
Less Net Income Attributable to Noncontrolling Interest, net of tax	0		0
Net Income (Loss)	6,111		10,001
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	72,653		114,337
Depreciation and amortization	(1,642)		(1,563)
Other operating expenses	(64,138)	[1]	(100,450)	[1]
Operating Income	6,873	[1]	12,324	[1]
Other income (deductions), net	(12)	[1]	(93)	[1]
Interest (expense) income, net	(804)		(804)
Net Income Including Noncontrolling Interest	6,057		11,427
Less Net Income Attributable to Noncontrolling Interest, net of tax	0		0
Net Income (Loss)	6,057		11,427
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	11,813		11,350
Depreciation and amortization	(1,863)		(1,834)
Other operating expenses	(3,414)	[1]	(3,212)	[1]
Operating Income	6,536	[1]	6,304	[1]
Other income (deductions), net	0	[1]	0	[1]
Interest (expense) income, net	(1,518)		(1,572)
Net Income Including Noncontrolling Interest	5,018		4,732
Less Net Income Attributable to Noncontrolling Interest, net of tax	0		0
Net Income (Loss)	5,018		4,732
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	1,125	[1]	1,483	[1]
Interest (expense) income, net	0		0
Net Income Including Noncontrolling Interest	1,125		1,483
Less Net Income Attributable to Noncontrolling Interest, net of tax	0		0
Net Income (Loss)	1,125		1,483
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	(12,677)		(14,401)
Depreciation and amortization	0		0
Other operating expenses	12,677	[1]	14,401	[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	(6,553)		(6,510)
Net Income (Loss)	(6,553)		(6,510)
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	110		112
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	2,720		3,619
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	9,847		10,670
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.