Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Operating revenues		$ 140,795	$ 135,135	$ 433,055	$ 474,145
Depreciation and amortization		(11,182)	(10,376)	(33,026)	(30,191)
Other operating expenses		(83,436)	(84,639)	(297,952)	(335,422)
Operating Income		46,177	40,120	102,077	108,532
Other income (deductions), net		2,564	2,636	7,115	10,736
Interest (expense) income, net		(5,036)	(5,141)	(15,135)	(14,550)
Income before income taxes		43,705	37,615	94,057	104,718
Income tax (provision) benefit		(15,351)	(14,286)	(33,946)	(39,585)
Net Income (Loss)		28,354	23,329	60,111	65,133
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		121,453	112,869	319,174	308,418
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		17,431	21,404	108,028	163,335
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		1,911	862	5,853	2,392
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		140,795	135,135	433,055	474,145
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		121,616	113,025	319,574	308,819
Depreciation and amortization		(7,584)	(6,931)	(22,372)	(19,909)
Other operating expenses		(80,202)	(74,573)	(239,963)	(229,286)
Operating Income		33,830	31,521	57,239	59,624
Other income (deductions), net		141	136	247	2,999
Interest (expense) income, net		(2,798)	(2,832)	(8,385)	(7,571)
Income before income taxes		31,173	28,825	49,101	55,052
Income tax (provision) benefit		(10,321)	(10,758)	(15,868)	(19,602)
Net Income (Loss)		20,852	18,067	33,233	35,450
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		21,286	23,018	116,899	170,465
Depreciation and amortization		(1,714)	(1,575)	(5,018)	(4,700)
Other operating expenses		(16,906)	(22,199)	(96,063)	(144,907)
Operating Income		2,666	(756)	15,818	20,858
Other income (deductions), net		(7)	8	(33)	(44)
Interest (expense) income, net		(804)	(808)	(2,398)	(2,429)
Income before income taxes		1,855	(1,556)	13,387	18,385
Income tax (provision) benefit		(732)	651	(5,370)	(7,378)
Net Income (Loss)		1,123	(905)	8,017	11,007
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,777	11,536	35,419	34,409
Depreciation and amortization		(1,872)	(1,858)	(5,601)	(5,547)
Other operating expenses		(36)	(35)	(122)	(105)
Operating Income		9,869	9,643	29,696	28,757
Other income (deductions), net		0	0	0	0
Interest (expense) income, net		(1,491)	(1,545)	(4,516)	(4,676)
Income before income taxes		8,378	8,098	25,180	24,081
Income tax (provision) benefit		(3,362)	(3,251)	(10,106)	(9,665)
Net Income (Loss)		5,016	4,847	15,074	14,416
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		(15)	0	(15)	0
Operating Income		(15)	0	(15)	0
Other income (deductions), net		2,397	2,423	6,568	7,306
Interest (expense) income, net		0	0	0	0
Income before income taxes		2,382	2,423	6,553	7,306
Income tax (provision) benefit		(962)	(963)	(2,637)	(2,924)
Net Income (Loss)		1,420	1,460	3,916	4,382
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0	0
Depreciation and amortization		(12)	(12)	(35)	(35)
Other operating expenses		(161)	(276)	(626)	(672)
Operating Income		(173)	(288)	(661)	(707)
Other income (deductions), net		33	69	333	475
Interest (expense) income, net		57	44	164	126
Income before income taxes		(83)	(175)	(164)	(106)
Income tax (provision) benefit		26	35	35	(16)
Net Income (Loss)		(57)	(140)	(129)	(122)
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(13,884)	(12,444)	(38,837)	(39,548)
Depreciation and amortization		0	0	0	0
Other operating expenses		13,884	12,444	38,837	39,548
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
Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		163	156	400	401
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		3,855	1,614	8,871	7,130
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		9,866	10,674	29,566	32,017
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		140,806	135,147	433,083	474,178
Depreciation and amortization		(11,170)	(10,364)	(32,991)	(30,156)
Other operating expenses	[1]	(97,686)	(97,712)	(328,571)	(370,962)
Operating Income	[1]	31,950	27,071	71,521	73,060
Other income (deductions), net	[1]	1,554	1,583	4,018	6,871
Interest (expense) income, net		(5,093)	(5,185)	(15,299)	(14,676)
Income tax (provision) benefit		(14,401)	(13,338)	(31,218)	(36,180)
Net Income Including Noncontrolling Interest		28,411	23,469	60,240	65,255
Less Net Income Attributable to Noncontrolling Interest, net of tax		(6,633)	(6,653)	(19,812)	(19,784)
Net Income (Loss)		21,778	16,816	40,428	45,471
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		121,460	112,875	319,191	308,435
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		17,435	21,410	108,039	163,351
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		1,911	862	5,853	2,392
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		140,806	135,147	433,083	474,178
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		121,616	113,025	319,574	308,819
Depreciation and amortization		(7,584)	(6,931)	(22,372)	(19,909)
Other operating expenses	[1]	(90,511)	(85,314)	(255,732)	(248,525)
Operating Income	[1]	23,521	20,780	41,470	40,385
Other income (deductions), net	[1]	129	119	148	2,636
Interest (expense) income, net		(2,798)	(2,832)	(8,385)	(7,571)
Net Income Including Noncontrolling Interest		20,852	18,067	33,233	35,450
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		20,852	18,067	33,233	35,450
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		21,286	23,018	116,899	170,465
Depreciation and amortization		(1,714)	(1,575)	(5,018)	(4,700)
Other operating expenses	[1]	(17,635)	(21,544)	(101,405)	(152,182)
Operating Income	[1]	1,937	(101)	10,476	13,583
Other income (deductions), net	[1]	(10)	4	(61)	(147)
Interest (expense) income, net		(804)	(808)	(2,398)	(2,429)
Net Income Including Noncontrolling Interest		1,123	(905)	8,017	11,007
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		1,123	(905)	8,017	11,007
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,777	11,536	35,419	34,409
Depreciation and amortization		(1,872)	(1,858)	(5,601)	(5,547)
Other operating expenses	[1]	(3,398)	(3,286)	(10,228)	(9,770)
Operating Income	[1]	6,507	6,392	19,590	19,092
Other income (deductions), net	[1]	0	0	0	0
Interest (expense) income, net		(1,491)	(1,545)	(4,516)	(4,676)
Net Income Including Noncontrolling Interest		5,016	4,847	15,074	14,416
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		5,016	4,847	15,074	14,416
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	[1]	(15)	0	(15)	0
Operating Income	[1]	(15)	0	(15)	0
Other income (deductions), net	[1]	1,435	1,460	3,931	4,382
Interest (expense) income, net		0	0	0	0
Net Income Including Noncontrolling Interest		1,420	1,460	3,916	4,382
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		1,420	1,460	3,916	4,382
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(13,873)	(12,432)	(38,809)	(39,515)
Depreciation and amortization		0	0	0	0
Other operating expenses	[1]	13,873	12,432	38,809	39,515
Operating Income	[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		(6,633)	(6,653)	(19,812)	(19,784)
Net Income (Loss)		(6,633)	(6,653)	(19,812)	(19,784)
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		156	150	383	384
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		3,851	1,608	8,860	7,114
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		9,866	10,674	29,566	32,017
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 MGE Consolidated Statement of Income.