Fair Value of Financial Instruments (Details-2) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Liabilities:
Derivative liability, collateral offset	$ 0	$ 100
Recurring [Member]
Assets:
Derivatives	2,121	1,005
Total Assets	3,023	1,797
Liabilities:
Derivatives	39,045	42,963	[1]
Deferred compensation	3,065	3,065
Total liabilities	42,110	46,028
Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	902	792
Recurring [Member] | Level 1 [Member]
Assets:
Derivatives	502	278
Total Assets	1,404	1,070
Liabilities:
Derivatives	94	210	[1]
Deferred compensation	0	0
Total liabilities	94	210
Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	902	792
Recurring [Member] | Level 2 [Member]
Assets:
Derivatives	0	0
Total Assets	0	0
Liabilities:
Derivatives	0	0	[1]
Deferred compensation	3,065	3,065
Total liabilities	3,065	3,065
Recurring [Member] | Level 2 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	0	0
Recurring [Member] | Level 3 [Member]
Assets:
Derivatives	1,619	727
Total Assets	1,619	727
Liabilities:
Derivatives	38,951	42,753	[1]
Deferred compensation	0	0
Total liabilities	38,951	42,753
Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	0	0
MGE [Member]
Liabilities:
Derivative liability, collateral offset	0	100
MGE [Member] | Recurring [Member]
Assets:
Derivatives	2,121	1,005
Total Assets	2,198	1,069
Liabilities:
Derivatives	39,045	42,963	[1]
Deferred compensation	3,065	3,065
Total liabilities	42,110	46,028
MGE [Member] | Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	77	64
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivatives	502	278
Total Assets	579	342
Liabilities:
Derivatives	94	210	[1]
Deferred compensation	0	0
Total liabilities	94	210
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	77	64
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivatives	0	0
Total Assets	0	0
Liabilities:
Derivatives	0	0	[1]
Deferred compensation	3,065	3,065
Total liabilities	3,065	3,065
MGE [Member] | Recurring [Member] | Level 2 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	0	0
MGE [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Derivatives	1,619	727
Total Assets	1,619	727
Liabilities:
Derivatives	38,951	42,753	[1]
Deferred compensation	0	0
Total liabilities	38,951	42,753
MGE [Member] | Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	$ 0	$ 0

[1] These amounts are shown gross and exclude $0.1 million of collateral that was posted against derivative positions with counterparties as of December 31, 2017.