Fair Value of Financial Instruments (Details-2) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Assets:
Available-for-sale securities	[1]	$ 9,363	$ 7,291
Recurring [Member]
Assets:
Derivative assets, net		1,042	1,005
Total Assets		1,890	1,797
Liabilities:
Derivative liabilities, net		32,872	42,963	[2]
Deferred compensation		3,078	3,065
Total Liabilities		35,950	46,028
Recurring [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		848	792
Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net		296	278
Total Assets		1,144	1,070
Liabilities:
Derivative liabilities, net		124	210	[2]
Deferred compensation		0	0
Total Liabilities		124	210
Recurring [Member] | Level 1 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		848	792
Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net		0	0
Total Assets		0	0
Liabilities:
Derivative liabilities, net		0	0	[2]
Deferred compensation		3,078	3,065
Total Liabilities		3,078	3,065
Recurring [Member] | Level 2 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		0	0
Recurring [Member] | Level 3 [Member]
Assets:
Derivative assets, net		746	727
Total Assets		746	727
Liabilities:
Derivative liabilities, net		32,748	42,753	[2]
Deferred compensation		0	0
Total Liabilities		32,748	42,753
Recurring [Member] | Level 3 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		0	0
MGE [Member]
Assets:
Available-for-sale securities	[1]	388	409
Liabilities:
Derivative liability, collateral offset		0	100
MGE [Member] | Recurring [Member]
Assets:
Derivative assets, net		1,042	1,005
Total Assets		1,085	1,069
Liabilities:
Derivative liabilities, net		32,872	42,963	[2]
Deferred compensation		3,078	3,065
Total Liabilities		35,950	46,028
MGE [Member] | Recurring [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		43	64
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net		296	278
Total Assets		339	342
Liabilities:
Derivative liabilities, net		124	210	[2]
Deferred compensation		0	0
Total Liabilities		124	210
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		43	64
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net		0	0
Total Assets		0	0
Liabilities:
Derivative liabilities, net		0	0	[2]
Deferred compensation		3,078	3,065
Total Liabilities		3,078	3,065
MGE [Member] | Recurring [Member] | Level 2 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		0	0
MGE [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Derivative assets, net		746	727
Total Assets		746	727
Liabilities:
Derivative liabilities, net		32,748	42,753	[2]
Deferred compensation		0	0
Total Liabilities		32,748	42,753
MGE [Member] | Recurring [Member] | Level 3 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		$ 0	$ 0

[1] Reflects modified retrospective application of new authoritative guidance related to Financial Instruments as described in Footnote 2. Prior to January 1, 2018, investments were considered available for sale securities. As of December 31, 2017, MGE Energy had available for sale securities with a cost basis of $6.7 million, gross unrealized gains of $0.7 million, and gross unrealized losses of less than $0.1 million. As of December 31, 2017, MGE had available for sale securities with a cost basis of $ 0.5 million and gross unrealized losses of less than $0.1 million.

[2] 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.