Fair Value of Financial Instruments (Details-1) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Carrying Amount [Member]
Assets:
Cash and cash equivalents		$ 94,267	$ 65,755
Liabilities:
Short-term debt - commercial paper		0	7,000
Long-term debt	[1]	396,562	399,690
Fair Value [Member]
Assets:
Cash and cash equivalents		94,267	65,755
Liabilities:
Short-term debt - commercial paper		0	7,000
Long-term debt	[1]	446,176	457,420
MGE [Member] | Carrying Amount [Member]
Assets:
Cash and cash equivalents		41,971	4,562
Liabilities:
Short-term debt - commercial paper		0	7,000
Long-term debt	[1]	396,562	399,690
MGE [Member] | Fair Value [Member]
Assets:
Cash and cash equivalents		41,971	4,562
Liabilities:
Short-term debt - commercial paper		0	7,000
Long-term debt	[1]	$ 446,176	$ 457,420

[1] *Includes long-term debt due within one year.