Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Current Assets:
Cash and cash equivalents	$ 45,894		$ 46,357
Receivable - margin account	766		1,818
Accounts receivable, less reserves	46,864	[1]	41,386	[2]
Other accounts receivables, less reserves	5,125	[3]	6,746	[3]
Unbilled revenues	26,761		28,262
Materials and supplies, at average cost	16,933		16,997
Fossil fuel	7,375		6,367
Stored natural gas, at average cost	2,195		14,980
Prepaid taxes	13,868		19,520
Regulatory assets - current	8,471		10,327
Deferred income taxes	14,260		23,483
Other current assets	7,431		6,694
Total Current Assets	195,943		222,937
Regulatory assets	214,496		218,853
Other deferred assets and other	7,222		7,075
Property, Plant, and Equipment:
Property, plant, and equipment, net	981,325		975,053
Construction work in progress	115,803		98,411
Total Property, Plant, and Equipment	1,097,128		1,073,464
Investments	65,651		64,595
Total Assets	1,580,440		1,586,924
Current Liabilities:
Long-term debt due within one year	3,365		3,013
Short-term debt	10,500		0
Accounts payable	39,586		43,518
Accrued interest and taxes	4,099		4,296
Accrued payroll related items	7,711		10,063
Derivative liabilities	8,880		9,270
Other current liabilities	10,605		5,637
Total Current Liabilities	84,746		75,797
Other Credits:
Deferred income taxes	272,511		270,410
Investment tax credit - deferred	1,466		1,520
Regulatory liabilities	22,598		24,538
Accrued pension and other postretirement benefits	133,380		162,835
Derivative liabilities	61,810		63,320
Other deferred liabilities and other	53,505		50,584
Total Other Credits	545,270		573,207
Capitalization:
Common shareholders equity	592,946		579,429
Long-term debt	357,478		358,491
Total Capitalization	950,424		937,920
Commitments and contingencies (see Footnote 8)	0		0
Total Liabilities and Capitalization	1,580,440		1,586,924
MGE [Member]
Current Assets:
Cash and cash equivalents	9,856		6,350
Receivable - margin account	766		1,818
Accounts receivable, less reserves	46,864	[1]	41,386	[2]
Affiliate receivables	619		634
Other accounts receivables, less reserves	5,124	[3]	6,732	[3]
Unbilled revenues	26,761		28,262
Materials and supplies, at average cost	16,933		16,997
Fossil fuel	7,375		6,367
Stored natural gas, at average cost	2,195		14,980
Prepaid taxes	18,108		23,561
Regulatory assets - current	8,471		10,327
Deferred income taxes	13,808		23,305
Other current assets	7,416		6,670
Total Current Assets	164,296		187,389
Affiliate receivable long-term	6,222		6,354
Regulatory assets	214,496		218,853
Other deferred assets and other	6,602		6,540
Property, Plant, and Equipment:
Property, plant, and equipment, net	980,820		974,549
Construction work in progress	115,803		98,411
Total Property, Plant, and Equipment	1,096,623		1,072,960
Investments	62,366		61,555
Total Assets	1,550,605		1,553,651
Current Liabilities:
Long-term debt due within one year	3,365		3,013
Short-term debt	10,500		0
Accounts payable	39,586		43,517
Affiliate payables	405		767
Accrued interest and taxes	3,699		4,248
Accrued payroll related items	7,711		10,063
Derivative liabilities	8,880		9,270
Other current liabilities	10,163		4,491
Total Current Liabilities	84,309		75,369
Other Credits:
Deferred income taxes	268,028		266,231
Investment tax credit - deferred	1,466		1,520
Regulatory liabilities	22,598		24,538
Accrued pension and other postretirement benefits	133,380		162,835
Derivative liabilities	61,810		63,320
Other deferred liabilities and other	53,505		50,581
Total Other Credits	540,787		569,025
Capitalization:
Common shareholders equity	449,057		433,296
Noncontrolling interest	118,974		117,470
Total Equity	568,031		550,766
Long-term debt	357,478		358,491
Total Capitalization	925,509		909,257
Commitments and contingencies (see Footnote 8)	0		0
Total Liabilities and Capitalization	$ 1,550,605		$ 1,553,651

[1] less reserves of $3,914

[2] less reserves of $3,885

[3] less reserves of $931