Pension Plans and Other Postretirement Benefits (Details-1) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Defined contribution plans [Abstract]
Defined contribution costs	$ 2,500,000		$ 2,300,000		$ 2,100,000
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	315,000,000
Fair value of plan assets at end of year	327,500,000		315,000,000
Amounts recognized in the consolidated balance sheets to reflect funded status of plans [Abstract]
Long-term asset	0		15,071,000
Long-term liability	(90,201,000)		(49,184,000)
Pension Benefits [Member]
Change in benefit obligations [Roll Forward]
Net benefit obligation at beginning of year	283,958,000		315,505,000
Service cost	6,179,000		7,705,000		7,139,000
Interest cost	13,574,000		12,656,000		12,704,000
Plan participants' contributions	0		0
Plan amendments	0		0
Actuarial (gain) loss	48,162,000	[1]	(40,335,000)	[1]
Gross benefits paid	(11,640,000)		(11,573,000)
Less: federal subsidy on benefits paid	0		0
Benefit obligation at end of year	340,233,000		283,958,000		315,505,000
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	277,398,000		212,277,000
Actual return on plan assets	21,907,000		45,816,000
Employer contributions	883,000		30,878,000
Plan participants' contributions	0		0
Gross benefits paid	(11,640,000)		(11,573,000)
Fair value of plan assets at end of year	288,548,000		277,398,000		212,277,000
Funded Status at December 31	(51,685,000)		(6,560,000)
Accumulated benefit obligation	304,000,000		254,500,000
Amounts recognized in the consolidated balance sheets to reflect funded status of plans [Abstract]
Long-term asset	0		15,071,000
Current liability	(1,025,000)		(945,000)
Long-term liability	(50,660,000)		(20,686,000)
Net asset (liability)	(51,685,000)		(6,560,000)
Amounts recognized in the consolidated balance sheets as regulatory asset [Abstract]
Net actuarial loss	85,102,000		37,499,000
Prior service (credit) cost	(413,000)		(209,000)
Transition obligation	0		0
Total	84,689,000		37,290,000
Projected benefit obligation in excess of plan assets [Abstract]
Projected benefit obligation with projected benefit obligation in excess of plan assets, end of year	340,233,000		21,631,000
Fair value of plan assets with projected benefit obligation in excess of plan assets, end of year	288,548,000		0
Accumulated benefit obligation in excess of plan assets [Abstract]
Projected benefit obligation with accumulated benefit obligation in excess of plan assets, end of year	340,233,000		21,631,000
Accumulated benefit obligation with accumulated benefit obligation in excess of plan assets, end of year	304,023,000		19,795,000
Fair value of plan assets with accumulated benefit obligation in excess of plan assets, end of year	288,548,000		0
Postretirement Benefits [Member]
Change in benefit obligations [Roll Forward]
Net benefit obligation at beginning of year	66,100,000		92,605,000
Service cost	1,339,000		2,380,000		2,528,000
Interest cost	3,166,000		3,871,000		4,431,000
Plan participants' contributions	708,000		665,000
Plan amendments	0		(20,915,000)	[2]
Actuarial (gain) loss	10,090,000	[1]	(9,687,000)	[1]
Gross benefits paid	(3,113,000)		(2,998,000)
Less: federal subsidy on benefits paid	188,000	[3]	179,000	[3]
Benefit obligation at end of year	78,478,000		66,100,000		92,605,000
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	37,602,000		32,124,000
Actual return on plan assets	2,558,000		5,000,000
Employer contributions	1,197,000		2,811,000
Plan participants' contributions	708,000		665,000
Gross benefits paid	(3,113,000)		(2,998,000)
Fair value of plan assets at end of year	38,952,000		37,602,000		32,124,000
Funded Status at December 31	(39,526,000)		(28,498,000)
Plan amendment, maximum percentage of 2013 employer contributions to be paid toward retiree medical premiums			175.00%
Medicare subsidy due to MGE	200,000		200,000
Amounts recognized in the consolidated balance sheets to reflect funded status of plans [Abstract]
Long-term asset	0		0
Current liability	(65,000)		(13,000)
Long-term liability	(39,461,000)		(28,485,000)
Net asset (liability)	(39,526,000)		(28,498,000)
Amounts recognized in the consolidated balance sheets as regulatory asset [Abstract]
Net actuarial loss	17,657,000		7,761,000
Prior service (credit) cost	(17,827,000)		(20,495,000)
Transition obligation	32,000		35,000
Total	$ (138,000)		$ (12,699,000)

[1] In 2014, lower discount rates and mortality table updates were the main drivers to the actuarial loss.

[2] In 2013, MGE capped the amount it pays each year toward retiree medical premiums at 175%of the 2013 employer contribution for qualified employees.

[3] In 2003, the Medicare Prescription Drug, Improvement and Modernization Act of 2003 was signed into law authorizing Medicare to provide prescription drug benefits to retirees. For the years ended December 31, 2014 and 2013, the subsidy due to MGE was $0.2 million.