Fair Value of Financial Instruments (Details-1) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Liabilities:
Unamortized discount and debt issuance costs, net		$ 4,270	$ 4,118
Carrying Amount [Member]
Assets:
Cash and cash equivalents		107,952	95,959
Liabilities:
Short-term debt - commercial paper		4,000	0
Long-Term debt	[1]	426,883	391,242
Fair Value [Member]
Assets:
Cash and cash equivalents		107,952	95,959
Liabilities:
Short-term debt - commercial paper		4,000	0
Long-Term debt	[1]	475,282	430,122
MGE [Member]
Liabilities:
Unamortized discount and debt issuance costs, net		4,270	4,118
MGE [Member] | Carrying Amount [Member]
Assets:
Cash and cash equivalents		5,951	10,768
Liabilities:
Short-term debt - commercial paper		4,000	0
Long-Term debt	[1]	426,883	391,242
MGE [Member] | Fair Value [Member]
Assets:
Cash and cash equivalents		5,951	10,768
Liabilities:
Short-term debt - commercial paper		4,000	0
Long-Term debt	[1]	$ 475,282	$ 430,122

[1] Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.3 million and $4.1 million at December 31, 2017 and 2016, respectively.