Consolidated Balance Sheets (Unaudited) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Current Assets:
Cash and cash equivalents	$ 75,330		$ 46,357
Receivable - margin account	1,357		1,818
Accounts receivable, less reserves	37,442	[1]	41,386	[2]
Other accounts receivables, less reserves	8,271	[3]	6,746	[4]
Unbilled revenues	20,290		28,262
Materials and supplies, at average cost	17,023		16,997
Fossil fuel	6,388		6,367
Stored natural gas, at average cost	18,004		14,980
Prepaid taxes	12,722		19,520
Regulatory assets - current	8,689		10,327
Deferred income taxes - current	0		23,483
Other current assets	8,349		6,694
Total Current Assets	213,865		222,937
Regulatory assets	213,068		218,853
Other deferred assets and other	6,436		7,075
Property, Plant, and Equipment:
Property, plant, and equipment, net	1,012,281		975,053
Construction work in progress	131,096		98,411
Total Property, Plant, and Equipment	1,143,377		1,073,464
Investments	66,965		64,595
Total Assets	1,643,711		1,586,924
Current Liabilities:
Long-term debt due within one year	4,082		3,013
Accounts payable	39,532		43,518
Accrued interest and taxes	4,041		4,296
Accrued payroll related items	9,819		10,063
Deferred income taxes	969		0
Regulatory liabilities - current	4,622		0
Derivative liabilities	9,310		9,270
Other current liabilities	6,337		5,637
Total Current Liabilities	78,712		75,797
Other Credits:
Deferred income taxes	278,899		270,410
Investment tax credit - deferred	1,466		1,520
Regulatory liabilities	25,757		24,538
Accrued pension and other postretirement benefits	133,730		162,835
Derivative liabilities	59,710		63,320
Other deferred liabilities and other	52,249		50,584
Total Other Credits	551,811		573,207
Capitalization:
Common shareholders equity	612,748		579,429
Long-term debt	400,440		358,491
Total Capitalization	1,013,188		937,920
Commitments and contingencies (see Footnote 8)	0		0
Total Liabilities and Capitalization	1,643,711		1,586,924
MGE [Member]
Current Assets:
Cash and cash equivalents	42,590		6,350
Receivable - margin account	1,357		1,818
Accounts receivable, less reserves	37,442	[1]	41,386	[2]
Affiliate receivables	532		634
Other accounts receivables, less reserves	8,220	[3]	6,732	[4]
Unbilled revenues	20,290		28,262
Materials and supplies, at average cost	17,023		16,997
Fossil fuel	6,388		6,367
Stored natural gas, at average cost	18,004		14,980
Prepaid taxes	17,334		23,561
Regulatory assets - current	8,689		10,327
Deferred income taxes - current	0		23,305
Other current assets	8,310		6,670
Total Current Assets	186,179		187,389
Affiliate receivable long-term	5,957		6,354
Regulatory assets	213,068		218,853
Other deferred assets and other	4,695		6,540
Property, Plant, and Equipment:
Property, plant, and equipment, net	1,012,150		974,549
Construction work in progress	131,096		98,411
Total Property, Plant, and Equipment	1,143,246		1,072,960
Investments	64,287		61,555
Total Assets	1,617,432		1,553,651
Current Liabilities:
Long-term debt due within one year	4,082		3,013
Accounts payable	39,532		43,517
Affiliate payables	40		767
Accrued interest and taxes	4,056		4,248
Accrued payroll related items	9,819		10,063
Deferred income taxes	1,379		0
Regulatory liabilities - current	4,622		0
Derivative liabilities	9,310		9,270
Other current liabilities	6,166		4,491
Total Current Liabilities	79,006		75,369
Other Credits:
Deferred income taxes	273,456		266,231
Investment tax credit - deferred	1,466		1,520
Regulatory liabilities	25,757		24,538
Accrued pension and other postretirement benefits	133,730		162,835
Derivative liabilities	59,710		63,320
Other deferred liabilities and other	52,251		50,581
Total Other Credits	546,370		569,025
Capitalization:
Common shareholders equity	473,682		433,296
Noncontrolling interest	117,934		117,470
Total Equity	591,616		550,766
Long-term debt	400,440		358,491
Total Capitalization	992,056		909,257
Commitments and contingencies (see Footnote 8)	0		0
Total Liabilities and Capitalization	$ 1,617,432		$ 1,553,651

[1] less reserves of $3,959

[2] less reserves of $3,885

[3] less reserves of $822

[4] less reserves of $931