Pension Plans and Other Postretirement Benefits (Details-1) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined contribution plans [Abstract]
Defined contribution costs		$ 2,800	$ 2,500	$ 2,300
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		327,500
Fair value of plan assets at end of year		330,886	327,500
Amounts recognized in the consolidated balance sheets to reflect funded status of plans [Abstract]
Long-term liability		(75,680)	(90,201)
Pension Benefits [Member]
Change in benefit obligations [Roll Forward]
Net benefit obligation at beginning of year		340,233	283,958
Service cost		7,263	6,179	7,705
Interest cost		13,766	13,574	12,656
Plan participants' contributions		0	0
Actuarial (gain) loss	[1]	(17,576)	48,162
Gross benefits paid		(11,121)	(11,640)
Less: federal subsidy on benefits paid		0	0
Benefit obligation at end of year		332,565	340,233	283,958
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		288,548	277,398
Actual return on plan assets		4,153	21,907
Employer contributions		9,136	883
Plan participants' contributions		0	0
Gross benefits paid		(11,121)	(11,640)
Fair value of plan assets at end of year		290,716	288,548	277,398
Funded Status at December 31		(41,849)	(51,685)
Accumulated benefit obligation		302,500	304,000
Amounts recognized in the consolidated balance sheets to reflect funded status of plans [Abstract]
Current liability		(966)	(1,025)
Long-term liability		(40,883)	(50,660)
Net liability		(41,849)	(51,685)
Amounts recognized in the consolidated balance sheets as regulatory asset [Abstract]
Net actuarial loss		80,660	85,102
Prior service (credit) cost		(436)	(413)
Transition obligation		0	0
Total		80,224	84,689
Projected benefit obligation in excess of plan assets [Abstract]
Projected benefit obligation with projected benefit obligation in excess of plan assets, end of year		332,565	340,233
Fair value of plan assets with projected benefit obligation in excess of plan assets, end of year		290,716	288,548
Accumulated benefit obligation in excess of plan assets [Abstract]
Projected benefit obligation with accumulated benefit obligation in excess of plan assets, end of year		332,565	340,233
Accumulated benefit obligation with accumulated benefit obligation in excess of plan assets, end of year		302,471	304,023
Fair value of plan assets with accumulated benefit obligation in excess of plan assets, end of year		290,716	288,548
Postretirement Benefits [Member]
Change in benefit obligations [Roll Forward]
Net benefit obligation at beginning of year		78,478	66,100
Service cost		1,559	1,339	2,380
Interest cost		3,075	3,166	3,871
Plan participants' contributions		741	708
Actuarial (gain) loss	[1]	(5,828)	10,090
Gross benefits paid		(3,280)	(3,113)
Less: federal subsidy on benefits paid	[2]	190	188
Benefit obligation at end of year		74,935	78,478	66,100
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year		38,952	37,602
Actual return on plan assets		603	2,558
Employer contributions		3,154	1,197
Plan participants' contributions		741	708
Gross benefits paid		(3,280)	(3,113)
Fair value of plan assets at end of year		40,170	38,952	$ 37,602
Funded Status at December 31		(34,765)	(39,526)
Medicare subsidy due to MGE		200	200
Amounts recognized in the consolidated balance sheets to reflect funded status of plans [Abstract]
Current liability		(52)	(65)
Long-term liability		(34,713)	(39,461)
Net liability		(34,765)	(39,526)
Amounts recognized in the consolidated balance sheets as regulatory asset [Abstract]
Net actuarial loss		13,086	17,657
Prior service (credit) cost		(15,158)	(17,827)
Transition obligation		29	32
Total		$ (2,043)	$ (138)

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

[2] 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, 2015 and 2014 , the subsidy due to MGE was $ 0.2 million .