Pension Plans and Other Postretirement Benefits (Details-1) - USD ($)		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018	Dec. 31, 2017
Defined contribution plans [Abstract]
Defined contribution costs		$ 4,400,000		$ 3,900,000	$ 3,500,000
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		366,301,000
Fair value of plan assets at end of year		434,922,000		366,301,000
Amounts recognized in the consolidated balance sheets to reflect funded status of plans [Abstract]
Long-term asset		13,630,000		0
Long-term liability		(68,665,000)		(67,483,000)
Pension Benefits [Member]
Change in benefit obligations [Roll Forward]
Net benefit obligation at beginning of year		360,288,000		391,269,000
Service cost		4,692,000	[1]	5,723,000	5,383,000
Interest cost		14,302,000	[1]	12,859,000	12,625,000
Plan participants' contributions		0		0
Actuarial loss (gain)	[2]	47,671,000		(34,439,000)
Gross benefits paid		(16,302,000)		(15,124,000)
Less: federal subsidy on benefits paid		0		0
Benefit obligation at end of year		410,651,000		360,288,000	391,269,000
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		323,780,000		361,651,000
Actual return on plan assets		76,766,000		(24,485,000)
Employer contributions		1,789,000		1,738,000
Plan participants' contributions		0		0
Gross benefits paid		(16,302,000)		(15,124,000)
Fair value of plan assets at end of year		386,033,000		323,780,000	361,651,000
Funded Status at December 31		(24,618,000)		(36,508,000)
Accumulated benefit obligation		383,000,000.0		335,800,000
Amounts recognized in the consolidated balance sheets to reflect funded status of plans [Abstract]
Long-term asset		13,630,000		0
Current liability		(1,688,000)		(1,732,000)
Long-term liability		(36,560,000)		(34,776,000)
Net liability		(24,618,000)		(36,508,000)
Amounts recognized in the consolidated balance sheets as regulatory asset [Abstract]
Net actuarial loss		79,290,000		92,978,000
Prior service (credit) cost		(268,000)		(385,000)
Transition obligation		0		0
Total		79,022,000		92,593,000
Projected benefit obligation in excess of plan assets [Abstract]
Projected benefit obligation with projected benefit obligation in excess of plan assets, end of year		38,247,000		360,288,000
Fair value of plan assets with projected benefit obligation in excess of plan assets, end of year		0		323,780,000
Accumulated benefit obligation in excess of plan assets [Abstract]
Accumulated benefit obligation with accumulated benefit obligation in excess of plan assets, end of year		35,798,000		31,200,000
Fair value of plan assets with accumulated benefit obligation in excess of plan assets, end of year		0		0
Postretirement Benefits [Member]
Change in benefit obligations [Roll Forward]
Net benefit obligation at beginning of year		75,161,000		82,290,000
Service cost		1,110,000	[1]	1,283,000	1,231,000
Interest cost		2,893,000	[1]	2,612,000	2,666,000
Plan participants' contributions		969,000		950,000
Actuarial loss (gain)	[2]	5,045,000		(7,555,000)
Gross benefits paid		(4,497,000)		(4,623,000)
Less: federal subsidy on benefits paid	[3]	220,000		204,000
Benefit obligation at end of year		80,901,000		75,161,000	82,290,000
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		42,521,000		48,470,000
Actual return on plan assets		9,277,000		(2,780,000)
Employer contributions		619,000		504,000
Plan participants' contributions		969,000		950,000
Gross benefits paid		(4,497,000)		(4,623,000)
Fair value of plan assets at end of year		48,889,000		42,521,000	$ 48,470,000
Funded Status at December 31		(32,012,000)		(32,640,000)
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		0		0
Long-term liability		(32,012,000)		(32,640,000)
Net liability		(32,012,000)		(32,640,000)
Amounts recognized in the consolidated balance sheets as regulatory asset [Abstract]
Net actuarial loss		8,659,000		10,569,000
Prior service (credit) cost		(4,484,000)		(7,153,000)
Transition obligation		17,000		21,000
Total		$ 4,192,000		$ 3,437,000

[1] MGE has deferred approximately $6.2 million of pension and other postretirement costs. The impact of the deferral has not been reflected in the table above. See Footnote 8 for further information.

[2] In 2019, lower discount rates were the main driver of the actuarial loss. However, in 2018, higher discount rates were the main driver of the actuarial gain.

[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, 2019 and 2018, the subsidy due to MGE was $0.2 million.