Fair Value of Financial Instruments (Details-2) - USD ($) $ in Thousands		Sep. 30, 2021	Dec. 31, 2020
Assets:
Collateral posted against derivative positions		$ 9,200	$ 0
Recurring [Member]
Assets:
Derivatives	[1]	14,210	806
Total Assets		15,334	2,556
Liabilities:
Derivatives		535	14,795	[1]
Deferred compensation		3,496	3,509
Total liabilities		4,031	18,304
Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		1,124	1,750
Recurring [Member] | Level 1 [Member]
Assets:
Derivatives	[1]	10,451	436
Total Assets		11,575	2,186
Liabilities:
Derivatives		365	370	[1]
Deferred compensation		0	0
Total liabilities		365	370
Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		1,124	1,750
Recurring [Member] | Level 2 [Member]
Assets:
Derivatives	[1]	0	0
Total Assets		0	0
Liabilities:
Derivatives		0	0	[1]
Deferred compensation		3,496	3,509
Total liabilities		3,496	3,509
Recurring [Member] | Level 2 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		0	0
Recurring [Member] | Level 3 [Member]
Assets:
Derivatives	[1]	3,759	370
Total Assets		3,759	370
Liabilities:
Derivatives		170	14,425	[1]
Deferred compensation		0	0
Total liabilities		170	14,425
Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		0	0
MGE [Member] | Recurring [Member]
Assets:
Derivatives	[1]	14,210	806
Total Assets		14,454	1,409
Liabilities:
Derivatives		535	14,795	[1]
Deferred compensation		3,496	3,509
Total liabilities		4,031	18,304
MGE [Member] | Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		244	603
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivatives	[1]	10,451	436
Total Assets		10,695	1,039
Liabilities:
Derivatives		365	370	[1]
Deferred compensation		0	0
Total liabilities		365	370
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		244	603
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivatives	[1]	0	0
Total Assets		0	0
Liabilities:
Derivatives		0	0	[1]
Deferred compensation		3,496	3,509
Total liabilities		3,496	3,509
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]	3,759	370
Total Assets		3,759	370
Liabilities:
Derivatives		170	14,425	[1]
Deferred compensation		0	0
Total liabilities		170	14,425
MGE [Member] | Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		$ 0	$ 0

[1] As of September 30, 2021, MGE received collateral of $9.2 million from counterparties under a master netting agreement for outstanding exchange traded derivative positions. The fair value of the derivative asset disclosed in this table has not been reduced for the collateral received. No collateral was posted against derivative positions owed to counterparties under a master netting agreement on the consolidated balance sheet as of December 31, 2020.