Segment Information (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Operating revenues		$ 126,463	$ 121,576	$ 283,286	$ 269,103
Depreciation and amortization		(13,275)	(11,114)	(26,234)	(22,146)
Other operating expenses		(86,637)	(82,250)	(197,591)	(189,214)
Operating income (loss)		26,551	28,212	59,461	57,743
Other income (deductions), net		2,614	2,179	5,065	4,621
Interest (expense) income, net		(4,886)	(4,957)	(9,780)	(9,957)
Income before income taxes		24,279	25,434	54,746	52,407
Income tax (provision) benefit		(8,736)	(9,284)	(19,903)	(19,229)
Net Income (Loss)		15,543	16,150	34,843	33,178
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		102,306	100,329	200,630	193,537
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		24,081	20,961	82,507	74,798
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		76	286	149	768
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		126,463	121,576	283,286	269,103
Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		102,187	100,896	200,406	194,560
Depreciation and amortization		(9,185)	(7,259)	(18,085)	(14,422)
Other operating expenses		(77,615)	(78,291)	(152,941)	(153,670)
Operating income (loss)		15,387	15,346	29,380	26,468
Other income (deductions), net		191	118	381	314
Interest (expense) income, net		(2,801)	(2,776)	(5,577)	(5,566)
Income before income taxes		12,777	12,688	24,184	21,216
Income tax (provision) benefit		(4,124)	(4,158)	(7,578)	(6,694)
Net Income (Loss)		8,653	8,530	16,606	14,522
Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		27,503	27,102	90,323	86,036
Depreciation and amortization		(2,232)	(2,015)	(4,445)	(3,996)
Other operating expenses		(23,153)	(21,295)	(73,730)	(69,036)
Operating income (loss)		2,118	3,792	12,148	13,004
Other income (deductions), net		(8)	(18)	(3)	(26)
Interest (expense) income, net		(805)	(799)	(1,604)	(1,607)
Income before income taxes		1,305	2,975	10,541	11,371
Income tax (provision) benefit		(521)	(1,195)	(4,225)	(4,554)
Net Income (Loss)		784	1,780	6,316	6,817
Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,183	11,205	22,326	22,664
Depreciation and amortization		(1,858)	(1,828)	(3,704)	(3,704)
Other operating expenses		(62)	(35)	(103)	(82)
Operating income (loss)		9,263	9,342	18,519	18,878
Other income (deductions), net		0	0	0	0
Interest (expense) income, net		(1,392)	(1,449)	(2,799)	(2,912)
Income before income taxes		7,871	7,893	15,720	15,966
Income tax (provision) benefit		(3,158)	(3,168)	(6,309)	(6,408)
Net Income (Loss)		4,713	4,725	9,411	9,558
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	(3)	0	(4)
Operating income (loss)		0	(3)	0	(4)
Other income (deductions), net		2,506	1,767	4,984	4,000
Interest (expense) income, net		0	0	0	0
Income before income taxes		2,506	1,764	4,984	3,996
Income tax (provision) benefit		(1,006)	(709)	(2,003)	(1,606)
Net Income (Loss)		1,500	1,055	2,981	2,390
Operating Segments [Member] | All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues		0	0	0	0
Depreciation and amortization		0	(12)	0	(24)
Other operating expenses		(217)	(253)	(586)	(579)
Operating income (loss)		(217)	(265)	(586)	(603)
Other income (deductions), net		(75)	312	(297)	333
Interest (expense) income, net		112	67	200	128
Income before income taxes		(180)	114	(683)	(142)
Income tax (provision) benefit		73	(54)	212	33
Net Income (Loss)		(107)	60	(471)	(109)
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(14,410)	(17,627)	(29,769)	(34,157)
Depreciation and amortization		0	0	0	0
Other operating expenses		14,410	17,627	29,769	34,157
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		(119)	567	(224)	1,023
Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		3,422	6,141	7,816	11,238
Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,107	10,919	22,177	21,896
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		126,462	121,589	283,298	269,132
Depreciation and amortization		(13,275)	(11,102)	(26,234)	(22,122)
Other operating expenses	[1]	(94,175)	(90,473)	(215,038)	(206,217)
Operating income (loss)	[1]	19,012	20,014	42,026	40,793
Other income (deductions), net	[1]	136	1,100	287	2,579
Interest (expense) income, net		(4,998)	(5,024)	(9,980)	(10,085)
Net Income Including Noncontrolling Interest		14,150	16,090	32,333	33,287
Less Net Income Attributable to Noncontrolling Interest, net of tax		(5,396)	(5,952)	(10,785)	(12,204)
Net Income (Loss)		8,754	10,138	21,548	21,083
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		102,306	100,336	200,634	193,550
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		24,080	20,967	82,515	74,814
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		76	286	149	768
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		126,462	121,589	283,298	269,132
MGE [Member] | Operating Segments [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		102,187	100,896	200,406	194,560
Depreciation and amortization		(9,185)	(7,259)	(18,085)	(14,422)
Other operating expenses	[1]	(81,702)	(82,405)	(160,448)	(160,284)
Operating income (loss)	[1]	11,300	11,232	21,873	19,854
Other income (deductions), net	[1]	154	74	310	234
Interest (expense) income, net		(2,801)	(2,776)	(5,577)	(5,566)
Net Income Including Noncontrolling Interest		8,653	8,530	16,606	14,522
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		8,653	8,530	16,606	14,522
MGE [Member] | Operating Segments [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		27,503	27,102	90,323	86,036
Depreciation and amortization		(2,232)	(2,015)	(4,445)	(3,996)
Other operating expenses	[1]	(23,664)	(22,476)	(77,935)	(73,567)
Operating income (loss)	[1]	1,607	2,611	7,943	8,473
Other income (deductions), net	[1]	(18)	(32)	(23)	(49)
Interest (expense) income, net		(805)	(799)	(1,604)	(1,607)
Net Income Including Noncontrolling Interest		784	1,780	6,316	6,817
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		784	1,780	6,316	6,817
MGE [Member] | Operating Segments [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,183	11,205	22,326	22,664
Depreciation and amortization		(1,858)	(1,828)	(3,704)	(3,704)
Other operating expenses	[1]	(3,220)	(3,203)	(6,412)	(6,490)
Operating income (loss)	[1]	6,105	6,174	12,210	12,470
Other income (deductions), net	[1]	0	0	0	0
Interest (expense) income, net		(1,392)	(1,449)	(2,799)	(2,912)
Net Income Including Noncontrolling Interest		4,713	4,725	9,411	9,558
Less Net Income Attributable to Noncontrolling Interest, net of tax		0	0	0	0
Net Income (Loss)		4,713	4,725	9,411	9,558
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]	0	(3)	0	(4)
Operating income (loss)	[1],[2]	0	(3)	0	(4)
Other income (deductions), net	[1],[2]	0	1,058	0	2,394
Interest (expense) income, net	[2]	0	0	0	0
Net Income Including Noncontrolling Interest	[2]	0	1,055	0	2,390
Less Net Income Attributable to Noncontrolling Interest, net of tax	[2]	0	0	0	0
Net Income (Loss)	[2]	0	1,055	0	2,390
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues		(14,411)	(17,614)	(29,757)	(34,128)
Depreciation and amortization		0	0	0	0
Other operating expenses	[1]	14,411	17,614	29,757	34,128
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		(5,396)	(5,952)	(10,785)	(12,204)
Net Income (Loss)		(5,396)	(5,952)	(10,785)	(12,204)
MGE [Member] | Consolidation Elimination Entries [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues		(119)	560	(228)	1,010
MGE [Member] | Consolidation Elimination Entries [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues		3,423	6,135	7,808	11,222
MGE [Member] | Consolidation Elimination Entries [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues		11,107	10,919	22,177	21,896
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.