Fair Value of Financial Instruments (Details-1) - USD ($) $ in Thousands		Mar. 31, 2019	Dec. 31, 2018
Fair Value Measurement [Domain]
Liabilities:
Unamortized discount and debt issuance costs, net		$ 4,400	$ 4,500
Carrying Amount [Member]
Assets:
Cash and cash equivalents		82,402	83,102
Liabilities:
Short-term debt - commercial paper		6,000	13,000
Long-term debt	[1]	501,303	502,431
Fair Value [Member]
Assets:
Cash and cash equivalents		82,402	83,102
Liabilities:
Short-term debt - commercial paper		6,000	13,000
Long-term debt	[1]	553,598	518,811
MGE [Member] | Fair Value Measurement [Domain]
Liabilities:
Unamortized discount and debt issuance costs, net		4,400	4,500
MGE [Member] | Carrying Amount [Member]
Assets:
Cash and cash equivalents		9,624	4,843
Liabilities:
Short-term debt - commercial paper		6,000	13,000
Long-term debt	[1]	501,303	502,431
MGE [Member] | Fair Value [Member]
Assets:
Cash and cash equivalents		9,624	4,843
Liabilities:
Short-term debt - commercial paper		6,000	13,000
Long-term debt	[1]	$ 553,598	$ 518,811

[1] Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.4 million and $4.5 million at March 31, 2019 and December 31, 2018, respectively.