Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Operating revenues		$ 136,717	$ 140,795	$ 405,820	$ 433,055
Depreciation and amortization		(11,212)	(11,182)	(33,358)	(33,026)
Other operating expenses		(78,978)	(83,436)	(268,192)	(297,952)
Operating income (loss)		46,527	46,177	104,270	102,077
Other income (deductions), net		2,105	2,564	6,726	7,115
Interest (expense) income, net		(5,038)	(5,036)	(14,995)	(15,135)
Income before income taxes		43,594	43,705	96,001	94,057
Income tax (provision) benefit		(15,714)	(15,351)	(34,943)	(33,946)
Net Income (Loss)		27,880	28,354	61,058	60,111
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		118,933	121,453	312,470	319,174
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		17,570	17,431	92,368	108,028
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		214	1,911	982	5,853
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		136,717	140,795	405,820	433,055
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		119,392	121,616	313,952	319,574
Depreciation and amortization		(7,332)	(7,584)	(21,754)	(22,372)
Other operating expenses		(77,010)	(80,202)	(230,680)	(239,963)
Operating income (loss)		35,050	33,830	61,518	57,239
Other income (deductions), net		178	141	492	247
Interest (expense) income, net		(2,855)	(2,798)	(8,421)	(8,385)
Income before income taxes		32,373	31,173	53,589	49,101
Income tax (provision) benefit		(11,290)	(10,321)	(17,984)	(15,868)
Net Income (Loss)		21,083	20,852	35,605	33,233
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		23,610	21,286	109,646	116,899
Depreciation and amortization		(2,047)	(1,714)	(6,043)	(5,018)
Other operating expenses		(19,292)	(16,906)	(88,328)	(96,063)
Operating income (loss)		2,271	2,666	15,275	15,818
Other income (deductions), net		13	(7)	(13)	(33)
Interest (expense) income, net		(818)	(804)	(2,425)	(2,398)
Income before income taxes		1,466	1,855	12,837	13,387
Income tax (provision) benefit		(494)	(732)	(5,048)	(5,370)
Net Income (Loss)		972	1,123	7,789	8,017
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,212	11,777	33,876	35,419
Depreciation and amortization		(1,833)	(1,872)	(5,537)	(5,601)
Other operating expenses		(33)	(36)	(115)	(122)
Operating income (loss)		9,346	9,869	28,224	29,696
Other income (deductions), net		0	0	0	0
Interest (expense) income, net		(1,436)	(1,491)	(4,348)	(4,516)
Income before income taxes		7,910	8,378	23,876	25,180
Income tax (provision) benefit		(3,175)	(3,362)	(9,583)	(10,106)
Net Income (Loss)		4,735	5,016	14,293	15,074
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		(13)	(15)	(17)	(15)
Operating income (loss)		(13)	(15)	(17)	(15)
Other income (deductions), net		2,023	2,397	6,023	6,568
Interest (expense) income, net		0	0	0	0
Income before income taxes		2,010	2,382	6,006	6,553
Income tax (provision) benefit		(812)	(962)	(2,418)	(2,637)
Net Income (Loss)		1,198	1,420	3,588	3,916
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0	0
Depreciation and amortization		0	(12)	(24)	(35)
Other operating expenses		(127)	(161)	(706)	(626)
Operating income (loss)		(127)	(173)	(730)	(661)
Other income (deductions), net		(109)	33	224	333
Interest (expense) income, net		71	57	199	164
Income before income taxes		(165)	(83)	(307)	(164)
Income tax (provision) benefit		57	26	90	35
Net Income (Loss)		(108)	(57)	(217)	(129)
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(17,497)	(13,884)	(51,654)	(38,837)
Depreciation and amortization		0	0	0	0
Other operating expenses		17,497	13,884	51,654	38,837
Operating income (loss)		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
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		459	163	1,482	400
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		6,040	3,855	17,278	8,871
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		10,998	9,866	32,894	29,566
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		136,728	140,806	405,860	433,083
Depreciation and amortization		(11,212)	(11,170)	(33,334)	(32,991)
Other operating expenses	[1]	(93,781)	(97,686)	(299,998)	(328,571)
Operating income (loss)	[1]	31,735	31,950	72,528	71,521
Other income (deductions), net	[1]	1,036	1,554	3,615	4,018
Interest (expense) income, net		(5,109)	(5,093)	(15,194)	(15,299)
Income tax (provision) benefit		(14,934)	(14,401)	(32,488)	(31,218)
Net Income Including Noncontrolling Interest		27,662	28,411	60,949	60,240
Less Net Income Attributable to Noncontrolling Interest, net of tax		(5,695)	(6,633)	(17,899)	(19,812)
Net Income (Loss)		21,967	21,778	43,050	40,428
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		118,938	121,460	312,488	319,191
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		17,576	17,435	92,390	108,039
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		214	1,911	982	5,853
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	[2]	0	0	0	0
MGE [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues		136,728	140,806	405,860	433,083
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		119,392	121,616	313,952	319,574
Depreciation and amortization		(7,332)	(7,584)	(21,754)	(22,372)
Other operating expenses	[1]	(88,282)	(90,511)	(248,566)	(255,732)
Operating income (loss)	[1]	23,778	23,521	43,632	41,470
Other income (deductions), net	[1]	160	129	394	148
Interest (expense) income, net		(2,855)	(2,798)	(8,421)	(8,385)
Net Income Including Noncontrolling Interest		21,083	20,852	35,605	33,233
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		21,083	20,852	35,605	33,233
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		23,610	21,286	109,646	116,899
Depreciation and amortization		(2,047)	(1,714)	(6,043)	(5,018)
Other operating expenses	[1]	(19,781)	(17,635)	(93,348)	(101,405)
Operating income (loss)	[1]	1,782	1,937	10,255	10,476
Other income (deductions), net	[1]	8	(10)	(41)	(61)
Interest (expense) income, net		(818)	(804)	(2,425)	(2,398)
Net Income Including Noncontrolling Interest		972	1,123	7,789	8,017
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		972	1,123	7,789	8,017
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,212	11,777	33,876	35,419
Depreciation and amortization		(1,833)	(1,872)	(5,537)	(5,601)
Other operating expenses	[1]	(3,208)	(3,398)	(9,698)	(10,228)
Operating income (loss)	[1]	6,171	6,507	18,641	19,590
Other income (deductions), net	[1]	0	0	0	0
Interest (expense) income, net		(1,436)	(1,491)	(4,348)	(4,516)
Net Income Including Noncontrolling Interest		4,735	5,016	14,293	15,074
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		4,735	5,016	14,293	15,074
MGE [Member] | Operating Segments [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	[2]	0	0	0	0
Depreciation and amortization	[2]	0	0	0	0
Other operating expenses	[1],[2]	4	(15)	0	(15)
Operating income (loss)	[1],[2]	4	(15)	0	(15)
Other income (deductions), net	[1],[2]	868	1,435	3,262	3,931
Interest (expense) income, net	[2]	0	0	0	0
Net Income Including Noncontrolling Interest	[2]	872	1,420	3,262	3,916
Less Net Income Attributable to Noncontrolling Interest, net of tax	[2]	0	0	0	0
Net Income (Loss)	[2]	872	1,420	3,262	3,916
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(17,486)	(13,873)	(51,614)	(38,809)
Depreciation and amortization		0	0	0	0
Other operating expenses	[1]	17,486	13,873	51,614	38,809
Operating income (loss)	[1]	0	0	0	0
Other income (deductions), net	[1]	0	0	0	0
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		(5,695)	(6,633)	(17,899)	(19,812)
Net Income (Loss)		(5,695)	(6,633)	(17,899)	(19,812)
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		454	156	1,464	383
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		6,034	3,851	17,256	8,860
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		10,998	9,866	32,894	29,566
MGE [Member] | Consolidation Elimination Entries [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	[2]	$ 0	$ 0	$ 0	$ 0

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

[2] As of July 31, 2016, MGE no longer consolidates MGE Energy's proportionate share of equity earnings in MGE Transco. See Footnote 3 for further discussion.