Fair Value of Financial Instruments (Details-2) - USD ($) $ in Thousands	Jun. 30, 2019		Dec. 31, 2018
Recurring [Member]
Assets:
Derivatives	$ 1,089	[1]	$ 1,042
Total Assets	2,168		1,890
Liabilities:
Derivatives	34,605		32,872
Deferred compensation	3,131		3,078
Total liabilities	37,736		35,950
Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	1,079		848
Recurring [Member] | Level 1 [Member]
Assets:
Derivatives	342	[1]	296
Total Assets	1,421		1,144
Liabilities:
Derivatives	521		124
Deferred compensation	0		0
Total liabilities	521		124
Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	1,079		848
Recurring [Member] | Level 2 [Member]
Assets:
Derivatives	0	[1]	0
Total Assets	0		0
Liabilities:
Derivatives	0		0
Deferred compensation	3,131		3,078
Total liabilities	3,131		3,078
Recurring [Member] | Level 2 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	0		0
Recurring [Member] | Level 3 [Member]
Assets:
Derivatives	747	[1]	746
Total Assets	747		746
Liabilities:
Derivatives	34,084		32,748
Deferred compensation	0		0
Total liabilities	34,084		32,748
Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	0		0
MGE [Member]
Liabilities:
Collateral posted against derivative positions	1,700
MGE [Member] | Recurring [Member]
Assets:
Derivatives	1,089	[1]	1,042
Total Assets	1,278		1,085
Liabilities:
Derivatives	34,605		32,872
Deferred compensation	3,131		3,078
Total liabilities	37,736		35,950
MGE [Member] | Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	189		43
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivatives	342	[1]	296
Total Assets	531		339
Liabilities:
Derivatives	521		124
Deferred compensation	0		0
Total liabilities	521		124
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	189		43
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivatives	0	[1]	0
Total Assets	0		0
Liabilities:
Derivatives	0		0
Deferred compensation	3,131		3,078
Total liabilities	3,131		3,078
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	747	[1]	746
Total Assets	747		746
Liabilities:
Derivatives	34,084		32,748
Deferred compensation	0		0
Total liabilities	34,084		32,748
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 million of collateral that was posted against derivative positions with counterparties as of June 30, 2019.