Fair Value of Financial Instruments (Details-2) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Liabilities:
Derivative liability, collateral offset		$ 100	$ 100
Recurring [Member]
Assets:
Derivatives		531	1,005
Total Assets		1,386	1,797
Liabilities:
Derivatives	[1]	41,772	42,963
Deferred compensation		3,110	3,065
Total liabilities		44,882	46,028
Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		855	792
Recurring [Member] | Level 1 [Member]
Assets:
Derivatives		284	278
Total Assets		1,139	1,070
Liabilities:
Derivatives	[1]	62	210
Deferred compensation		0	0
Total liabilities		62	210
Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		855	792
Recurring [Member] | Level 2 [Member]
Assets:
Derivatives		0	0
Total Assets		0	0
Liabilities:
Derivatives	[1]	0	0
Deferred compensation		3,110	3,065
Total liabilities		3,110	3,065
Recurring [Member] | Level 2 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		0	0
Recurring [Member] | Level 3 [Member]
Assets:
Derivatives		247	727
Total Assets		247	727
Liabilities:
Derivatives	[1]	41,710	42,753
Deferred compensation		0	0
Total liabilities		41,710	42,753
Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		0	0
MGE [Member]
Liabilities:
Derivative liability, collateral offset		100	100
MGE [Member] | Recurring [Member]
Assets:
Derivatives		531	1,005
Total Assets		596	1,069
Liabilities:
Derivatives	[1]	41,772	42,963
Deferred compensation		3,110	3,065
Total liabilities		44,882	46,028
MGE [Member] | Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		65	64
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivatives		284	278
Total Assets		349	342
Liabilities:
Derivatives	[1]	62	210
Deferred compensation		0	0
Total liabilities		62	210
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		65	64
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivatives		0	0
Total Assets		0	0
Liabilities:
Derivatives	[1]	0	0
Deferred compensation		3,110	3,065
Total liabilities		3,110	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		247	727
Total Assets		247	727
Liabilities:
Derivatives	[1]	41,710	42,753
Deferred compensation		0	0
Total liabilities		41,710	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 March 31, 2018 and December 31, 2017.