Fair Value of Financial Instruments (Details-1) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
MGE Energy [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Assets:
Cash and cash equivalents	$ 32,054	$ 7,110
Liabilities:
Short-term debt - bank loans	0	19,000
Short-term debt - commercial paper	0	3,500
Long-term debt	365,806	336,973
MGE Energy [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Assets:
Cash and cash equivalents	32,054	7,110
Liabilities:
Short-term debt - bank loans	0	19,000
Short-term debt - commercial paper	0	3,500
Long-term debt	384,339	356,395
MGE [Member] | Carrying Reported Amount Fair Value Disclosure [Member]
Assets:
Cash and cash equivalents	17,248	4,494
Liabilities:
Short-term debt - commercial paper	0	3,500
Long-term debt	365,806	336,973
MGE [Member] | Estimate Of Fair Value Fair Value Disclosure [Member]
Assets:
Cash and cash equivalents	17,248	4,494
Liabilities:
Short-term debt - commercial paper	0	3,500
Long-term debt	$ 384,339	$ 356,395