Fair Value of Financial Instruments (Details-1) - USD ($) $ in Thousands		Sep. 30, 2021	Dec. 31, 2020
Liabilities:
Unamortized discount and debt issuance costs, net		$ 4,500	$ 4,100
Carrying Amount [Member]
Assets:
Cash and cash equivalents		70,454	44,738
Liabilities:
Short-term debt - commercial paper		0	52,500
Long-term debt	[1]	624,653	528,220
Fair Value [Member]
Assets:
Cash and cash equivalents		70,454	44,738
Liabilities:
Short-term debt - commercial paper		0	52,500
Long-term debt	[1]	692,987	639,271
MGE [Member]
Liabilities:
Unamortized discount and debt issuance costs, net		4,500	4,100
MGE [Member] | Carrying Amount [Member]
Assets:
Cash and cash equivalents		57,003	4,103
Liabilities:
Short-term debt - commercial paper		0	52,500
Long-term debt	[1]	624,653	528,220
MGE [Member] | Fair Value [Member]
Assets:
Cash and cash equivalents		57,003	4,103
Liabilities:
Short-term debt - commercial paper		0	52,500
Long-term debt	[1]	$ 692,987	$ 639,271

[1] Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.5 million and $4.1 million as of September 30, 2021, and December 31, 2020, respectively.