Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Current Assets:
Cash and cash equivalents	$ 46,357		$ 41,169
Receivable - margin account	1,818		2,477
Accounts receivable, less reserves	41,386	[1]	36,744	[2]
Other accounts receivables, less reserves	6,746	[3]	5,318	[4]
Unbilled revenues	28,262		25,754
Materials and supplies, at average cost	16,997		14,758
Fossil fuel	6,367		5,468
Stored natural gas, at average cost	14,980		19,575
Prepaid taxes	19,520		22,251
Regulatory assets - current	10,327		7,347
Deferred income taxes	23,483		0
Other current assets	6,694		8,270
Total Current Assets	222,937		189,131
Other long-term receivables	1,102		1,494
Regulatory assets	218,853		205,835
Other deferred assets and other	5,973		6,524
Property, Plant, and Equipment:
Property, plant, and equipment, net	975,053		961,511
Construction work in progress	98,411		34,055
Total Property, Plant, and Equipment	1,073,464		995,566
Investments	64,595		60,332
Total Assets	1,586,924		1,458,882
Current Liabilities:
Long-term debt due within one year	3,013		2,667
Short-term debt	0		0
Accounts payable	43,518		34,532
Accrued interest and taxes	4,296		4,085
Accrued payroll related items	10,063		9,987
Deferred income taxes	0		3,020
Derivative liabilities	9,270		7,483
Other current liabilities	5,637		1,300
Total Current Liabilities	75,797		63,074
Other Credits:
Deferred income taxes	270,410		199,850
Investment tax credit - deferred	1,520		1,780
Regulatory liabilities	24,538		20,463
Accrued pension and other postretirement benefits	162,835		183,622
Derivative liabilities	63,320		35,046
Other deferred liabilities and other	50,584		43,192
Total Other Credits	573,207		483,953
Common shareholders' equity:
Common stock	23,114	[5]	23,114	[5]
Additional paid-in capital	316,268		316,268
Retained earnings	239,953		211,458
Accumulated other comprehensive income, net of tax	94		112
Total Common Shareholders' Equity	579,429		550,952
Long-term debt	358,491		360,903
Total Capitalization	937,920		911,855
Commitments and contingencies (see Footnote 18)	0		0
Total Liabilities and Capitalization	1,586,924		1,458,882
MGE [Member]
Current Assets:
Cash and cash equivalents	6,350		13,898
Receivable - margin account	1,818		2,477
Accounts receivable, less reserves	41,386	[1]	35,765	[2]
Affiliate receivables	634		605
Other accounts receivables, less reserves	6,732	[3]	5,301	[4]
Unbilled revenues	28,262		25,754
Materials and supplies, at average cost	16,997		14,758
Fossil fuel	6,367		5,468
Stored natural gas, at average cost	14,980		19,575
Prepaid taxes	23,561		21,977
Regulatory assets - current	10,327		7,347
Deferred income taxes	23,305		0
Other current assets	6,670		8,245
Total Current Assets	187,389		161,170
Other long-term receivables	696		914
Affiliate receivable long-term	6,354		6,884
Regulatory assets	218,853		205,835
Other deferred assets and other	5,844		6,372
Property, Plant, and Equipment:
Property, plant, and equipment, net	974,549		961,007
Construction work in progress	98,411		34,055
Total Property, Plant, and Equipment	1,072,960		995,062
Investments	61,555		57,556
Total Assets	1,553,651		1,433,793
Current Liabilities:
Long-term debt due within one year	3,013		2,667
Accounts payable	43,517		34,532
Affiliate payables	767		2,152
Accrued interest and taxes	4,248		4,037
Accrued payroll related items	10,063		9,987
Deferred income taxes	0		3,020
Derivative liabilities	9,270		7,483
Other current liabilities	4,491		1,082
Total Current Liabilities	75,369		64,960
Other Credits:
Deferred income taxes	266,231		196,550
Investment tax credit - deferred	1,520		1,780
Regulatory liabilities	24,538		20,463
Accrued pension and other postretirement benefits	162,835		183,622
Derivative liabilities	63,320		35,046
Other deferred liabilities and other	50,581		43,192
Total Other Credits	569,025		480,653
Common shareholders' equity:
Common stock	17,348	[6]	17,348	[6]
Additional paid-in capital	192,417		192,417
Retained earnings	223,527		203,114
Accumulated other comprehensive income, net of tax	4		47
Total Common Shareholders' Equity	433,296		412,926
Noncontrolling interest	117,470		114,351
Total Equity	550,766		527,277
Long-term debt	358,491		360,903
Total Capitalization	909,257		888,180
Commitments and contingencies (see Footnote 18)	0		0
Total Liabilities and Capitalization	$ 1,553,651		$ 1,433,793

[1] less reserves of $3,885

[2] less reserves of $3,662

[3] less reserves of $931

[4] less reserves of $439

[5] $1 par value - 50,000 shares authorized; 23,114 shares issued and outstanding

[6] $1 par value - 50,000 shares authorized; 17,348 shares outstanding