Fair Value of Financial Instruments (Details-1) - USD ($) $ in Thousands		Dec. 31, 2018	Dec. 31, 2017
Liabilities:
Unamortized discount and debt issuance costs, net		$ 4,535	$ 4,270
Carrying Amount [Member]
Assets:
Cash and cash equivalents		83,102	107,952
Liabilities:
Short-term debt - commercial paper		13,000	4,000
Long-Term debt	[1]	502,431	426,883
Fair Value [Member]
Assets:
Cash and cash equivalents		83,102	107,952
Liabilities:
Short-term debt - commercial paper		13,000	4,000
Long-Term debt	[1]	518,811	475,282
MGE [Member] | Carrying Amount [Member]
Assets:
Cash and cash equivalents		4,843	5,951
Liabilities:
Short-term debt - commercial paper		13,000	4,000
Long-Term debt	[1]	502,431	426,883
MGE [Member] | Fair Value [Member]
Assets:
Cash and cash equivalents		4,843	5,951
Liabilities:
Short-term debt - commercial paper		13,000	4,000
Long-Term debt	[1]	$ 518,811	$ 475,282

[1] Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.5 million and $4.3 million at December 31, 2018 and 2017, respectively.