Fair Value of Financial Instruments (Details-1) - USD ($) $ in Thousands		Sep. 30, 2017	Dec. 31, 2016
Fair Value Measurement [Domain]
Liabilities:
Unamortized discount and debt issuance costs, net		$ 4,100	$ 4,100
Carrying Amount [Member]
Assets:
Cash and cash equivalents		104,733	95,959
Liabilities:
Short-term debt - commercial paper		7,000	0
Long-term debt	[1]	397,981	391,242
Fair Value [Member]
Assets:
Cash and cash equivalents		104,733	95,959
Liabilities:
Short-term debt - commercial paper		7,000	0
Long-term debt	[1]	444,195	430,122
MGE [Member] | Fair Value Measurement [Domain]
Liabilities:
Unamortized discount and debt issuance costs, net		4,100	4,100
MGE [Member] | Carrying Amount [Member]
Assets:
Cash and cash equivalents		1,954	10,768
Liabilities:
Short-term debt - commercial paper		7,000	0
Long-term debt	[1]	397,981	391,242
MGE [Member] | Fair Value [Member]
Assets:
Cash and cash equivalents		1,954	10,768
Liabilities:
Short-term debt - commercial paper		7,000	0
Long-term debt	[1]	$ 444,195	$ 430,122

[1] Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.1 million at September 30, 2017, and December 31, 2016.