Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating revenues	$ 167,237	$ 149,259
Interdepartmental revenues	0	0
Total operating revenues	167,237	149,259
Depreciation and amortization	(9,624)	(9,624)
Other operating expenses	(119,985)	(111,191)
Operating Income	37,628	28,444
Other (deductions) income, net	3,309	2,570
Interest (expense) income, net	(4,675)	(5,104)
Income before income taxes	36,262	25,910
Income tax provision	(13,678)	(9,862)
Net Income (Loss)	22,584	16,048
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,580,440		1,586,924
Capital Expenditures	29,164		98,435
Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	93,494	89,936
Interdepartmental revenues	109	109
Total operating revenues	93,603	90,045
Depreciation and amortization	(6,400)	(6,478)
Other operating expenses	(74,925)	(72,788)
Operating Income	12,278	10,779
Other (deductions) income, net	575	164
Interest (expense) income, net	(2,404)	(2,727)
Income before income taxes	10,449	8,216
Income tax provision	(3,433)	(2,785)
Net Income (Loss)	7,016	5,431
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	904,578		888,444
Capital Expenditures	27,007		81,965
Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	72,467	57,019
Interdepartmental revenues	4,876	2,986
Total operating revenues	77,343	60,005
Depreciation and amortization	(1,425)	(1,370)
Other operating expenses	(60,437)	(49,741)
Operating Income	15,481	8,894
Other (deductions) income, net	162	46
Interest (expense) income, net	(678)	(769)
Income before income taxes	14,965	8,171
Income tax provision	(5,989)	(3,238)
Net Income (Loss)	8,976	4,933
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	275,815		285,468
Capital Expenditures	1,689		13,812
Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,276	2,304
Interdepartmental revenues	10,573	8,676
Total operating revenues	11,849	10,980
Depreciation and amortization	(1,799)	(1,776)
Other operating expenses	(37)	(12)
Operating Income	10,013	9,192
Other (deductions) income, net	0	0
Interest (expense) income, net	(1,613)	(1,645)
Income before income taxes	8,400	7,547
Income tax provision	(3,257)	(3,029)
Net Income (Loss)	5,143	4,518
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	324,894		323,216
Capital Expenditures	468		2,658
Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Interdepartmental revenues	0	0
Total operating revenues	0	0
Depreciation and amortization	0	0
Other operating expenses	0	0
Operating Income	0	0
Other (deductions) income, net	2,396	2,242
Interest (expense) income, net	0	0
Income before income taxes	2,396	2,242
Income tax provision	(971)	(910)
Net Income (Loss)	1,425	1,332
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	61,826		61,064
Capital Expenditures	0		0
All Others [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Interdepartmental revenues	0	0
Total operating revenues	0	0
Depreciation and amortization	0	0
Other operating expenses	(144)	(421)
Operating Income	(144)	(421)
Other (deductions) income, net	176	118
Interest (expense) income, net	20	37
Income before income taxes	52	(266)
Income tax provision	(28)	100
Net Income (Loss)	24	(166)
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	409,602		413,291
Capital Expenditures	0		0
Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Interdepartmental revenues	(15,558)	(11,771)
Total operating revenues	(15,558)	(11,771)
Depreciation and amortization	0	0
Other operating expenses	15,558	11,771
Operating Income	0	0
Other (deductions) income, net	0	0
Interest (expense) income, net	0	0
Income before income taxes	0	0
Income tax provision	0	0
Net Income (Loss)	0	0
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	(408,175)		(403,118)
Capital Expenditures	0		0
Assets Not Allocated [Member]
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	11,900		18,559
Capital Expenditures	0		0
MGE [Member]
Segment Reporting Information [Line Items]
Operating revenues	167,237	149,259
Interdepartmental revenues	0	0
Total operating revenues	167,237	149,259
Depreciation and amortization	(9,624)	(9,624)
Other operating expenses	(132,710)	(119,739)
Operating Income	24,903	19,896
Other (deductions) income, net	2,352	1,459
Interest (expense) income, net	(4,695)	(5,141)
Income tax provision	(12,870)	(8,969)
Net Income Including Noncontrolling Interest	22,560	16,214
Less Net Income Attributable to Noncontrolling Interest, net of tax	(6,826)	(6,072)
Net Income (Loss)	15,734	10,142
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	1,550,605		1,553,651
Capital Expenditures	29,164		98,435
MGE [Member] | Electric [Member]
Segment Reporting Information [Line Items]
Operating revenues	93,494	89,936
Interdepartmental revenues	109	109
Total operating revenues	93,603	90,045
Depreciation and amortization	(6,400)	(6,478)
Other operating expenses	(78,506)	(75,508)
Operating Income	8,697	8,059
Other (deductions) income, net	723	99
Interest (expense) income, net	(2,404)	(2,727)
Net Income Including Noncontrolling Interest	7,016	5,431
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0
Net Income (Loss)	7,016	5,431
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	904,578		888,444
Capital Expenditures	27,007		81,965
MGE [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	72,467	57,019
Interdepartmental revenues	4,876	2,986
Total operating revenues	77,343	60,005
Depreciation and amortization	(1,425)	(1,370)
Other operating expenses	(66,468)	(52,961)
Operating Income	9,450	5,674
Other (deductions) income, net	204	28
Interest (expense) income, net	(678)	(769)
Net Income Including Noncontrolling Interest	8,976	4,933
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0
Net Income (Loss)	8,976	4,933
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	275,815		285,468
Capital Expenditures	1,689		13,812
MGE [Member] | Non Regulated Energy [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,276	2,304
Interdepartmental revenues	10,573	8,676
Total operating revenues	11,849	10,980
Depreciation and amortization	(1,799)	(1,776)
Other operating expenses	(3,294)	(3,041)
Operating Income	6,756	6,163
Other (deductions) income, net	0	0
Interest (expense) income, net	(1,613)	(1,645)
Net Income Including Noncontrolling Interest	5,143	4,518
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0
Net Income (Loss)	5,143	4,518
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	324,844		323,166
Capital Expenditures	468		2,658
MGE [Member] | Transmission Investment [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Interdepartmental revenues	0	0
Total operating revenues	0	0
Depreciation and amortization	0	0
Other operating expenses	0	0
Operating Income	0	0
Other (deductions) income, net	1,425	1,332
Interest (expense) income, net	0	0
Net Income Including Noncontrolling Interest	1,425	1,332
Less Net Income Attributable to Noncontrolling Interest, net of tax	0	0
Net Income (Loss)	1,425	1,332
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	61,826		61,064
Capital Expenditures	0		0
MGE [Member] | Consolidation Elimination Entries [Member]
Segment Reporting Information [Line Items]
Operating revenues	0	0
Interdepartmental revenues	(15,558)	(11,771)
Total operating revenues	(15,558)	(11,771)
Depreciation and amortization	0	0
Other operating expenses	15,558	11,771
Operating Income	0	0
Other (deductions) income, net	0	0
Interest (expense) income, net	0	0
Net Income Including Noncontrolling Interest	0	0
Less Net Income Attributable to Noncontrolling Interest, net of tax	(6,826)	(6,072)
Net Income (Loss)	(6,826)	(6,072)
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	(28,358)		(23,050)
Capital Expenditures	0		0
MGE [Member] | Assets Not Allocated [Member]
Segment Reporting Assets And Capital Expenditures [Abstract]
Assets	11,900		18,559
Capital Expenditures	$ 0		$ 0