Fair Value of Financial Instruments (Details-1) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015
Carrying Amount [Member]
Assets:
Cash and cash equivalents		$ 111,585	$ 81,384
Liabilities:
Long-term debt	[1]	392,316	395,508
Unamortized discount and debt issuance costs, net		4,200	4,500
Fair Value [Member]
Assets:
Cash and cash equivalents		111,585	81,384
Liabilities:
Long-term debt	[1]	463,849	435,767
Unamortized discount and debt issuance costs, net		4,200	4,500
MGE [Member] | Carrying Amount [Member]
Assets:
Cash and cash equivalents		31,558	26,760
Liabilities:
Long-term debt	[1]	392,316	395,508
Unamortized discount and debt issuance costs, net		4,200	4,500
MGE [Member] | Fair Value [Member]
Assets:
Cash and cash equivalents		31,558	26,760
Liabilities:
Long-term debt	[1]	463,849	435,767
Unamortized discount and debt issuance costs, net		$ 4,200	$ 4,500

[1] Includes long-term debt due within one year. Excludes debt issuance costs and unamortized discount of $4.2 million and $4.5 million at September 30, 2016, and December 31, 2015, respectively.