Fair Value of Financial Instruments (Details-1) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Carrying Amount [Member]
Assets:
Cash and cash equivalents	$ 41,169	$ 7,110
Liabilities:
Short-term debt - bank loans	0	19,000
Short-term debt - commercial paper	0	3,500
Long-term debt	364,473	336,973
Fair Value [Member]
Assets:
Cash and cash equivalents	41,169	7,110
Liabilities:
Short-term debt - bank loans	0	19,000
Short-term debt - commercial paper	0	3,500
Long-term debt	432,515	356,395
MGE [Member] | Carrying Amount [Member]
Assets:
Cash and cash equivalents	13,898	4,494
Liabilities:
Short-term debt - bank loans	0	3,500
Long-term debt	364,473	336,973
MGE [Member] | Fair Value [Member]
Assets:
Cash and cash equivalents	13,898	4,494
Liabilities:
Short-term debt - bank loans	0	3,500
Long-term debt	$ 432,515	$ 356,395