Fair Value of Financial Instruments (Details-1) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 31, 2017
Fair Value Measurement [Domain]
Liabilities:
Unamortized discount and debt issuance costs, net		$ 4,200	$ 4,300
Carrying Amount [Member]
Assets:
Cash and cash equivalents		101,157	107,952
Liabilities:
Short-term debt - commercial paper		3,000	4,000
Long-term debt	[1]	425,780	426,883
Fair Value [Member]
Assets:
Cash and cash equivalents		101,157	107,952
Liabilities:
Short-term debt - commercial paper		3,000	4,000
Long-term debt	[1]	462,151	475,282
MGE [Member] | Fair Value Measurement [Domain]
Liabilities:
Unamortized discount and debt issuance costs, net		4,200	4,300
MGE [Member] | Carrying Amount [Member]
Assets:
Cash and cash equivalents		4,152	5,951
Liabilities:
Short-term debt - commercial paper		3,000	4,000
Long-term debt	[1]	425,780	426,883
MGE [Member] | Fair Value [Member]
Assets:
Cash and cash equivalents		4,152	5,951
Liabilities:
Short-term debt - commercial paper		3,000	4,000
Long-term debt	[1]	$ 462,151	$ 475,282

[1] Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.2 million and $4.3 million at March 31, 2018 and December 31, 2017, respectively.