Pension Plans and Other Postretirement Benefits (Details-1) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined contribution plans [Abstract]
Defined contribution costs	$ 1,800,000	$ 1,600,000	$ 1,300,000
Health care cost trend rates [Abstract]
Health care cost trend rate assumed for next year	8.00%	7.00%
Ultimate trend rate	5.00%	5.00%
Year that rate reaches ultimate trend rate	2018	2015
How 1% increase or decrease in health care cost trends could impact postretirement benefits [Abstract]
1% increase	16,510,000
1% decrease	(13,310,000)
Medicare prescription drug benefits to retirees [Abstract]
Medicare subsidy due to MGE	200,000
Pension Benefits [Member]
Change in benefit obligations [Roll Forward]
Net benefit obligation at beginning of year	232,900,000	208,780,000
Service cost	6,013,000	5,554,000	5,235,000
Interest cost	12,281,000	11,928,000	11,430,000
Plan participants' contributions	0	0
Plan amendments	0	0
Actuarial (gain) loss	40,925,000	14,366,000
Special termination benefits	13,000	0	0
Gross benefits paid	(8,464,000)	(7,728,000)
Less: federal subsidy on benefits paid	0	0
Benefit obligation at end of year	283,668,000	232,900,000	208,780,000
Accumulated benefit obligation	245,900,000	200,900,000
Weighted-average assumptions used to determine benefit obligations [Abstract]
Discount rate	4.50%	5.36%
Rate of compensation increase	4.59%	4.59%
Postretirement Benefits [Member]
Change in benefit obligations [Roll Forward]
Net benefit obligation at beginning of year	71,762,000	66,138,000
Service cost	1,920,000	1,849,000	1,783,000
Interest cost	3,980,000	3,926,000	3,801,000
Plan participants' contributions	626,000	569,000
Plan amendments	0	0
Actuarial (gain) loss	22,211,000	1,866,000
Special termination benefits	0	0	0
Gross benefits paid	(3,022,000)	(2,771,000)
Less: federal subsidy on benefits paid	167,000	185,000
Benefit obligation at end of year	$ 97,644,000	$ 71,762,000	$ 66,138,000
Weighted-average assumptions used to determine benefit obligations [Abstract]
Discount rate	4.55%	5.42%