Fair Value of Financial Instruments (Details-2) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Assets:
Exchange-traded investments	$ 320,000	$ 350,000
Total Assets	320,000	350,000
Liabilities:
Derivatives, net	72,329,000	42,356,000
Deferred compensation	2,010,000	1,725,000
Total Liabilities	74,339,000	44,081,000
Derivative collateral	0	3,000,000
Deferred compensation interest calculation [Abstract]
U.S Treasury Bills maturity	26
Increase compounded monthly	1.00%
Minimum annual rate	7.00%
Level 1 [Member]
Assets:
Exchange-traded investments	320,000	350,000
Total Assets	320,000	350,000
Liabilities:
Derivatives, net	(17,000)	1,695,000
Deferred compensation	0	0
Total Liabilities	(17,000)	1,695,000
Level 2 [Member]
Assets:
Exchange-traded investments	0	0
Total Assets	0	0
Liabilities:
Derivatives, net	0	0
Deferred compensation	2,010,000	1,725,000
Total Liabilities	2,010,000	1,725,000
Level 3 [Member]
Assets:
Exchange-traded investments	0	0
Total Assets	0	0
Liabilities:
Derivatives, net	72,346,000	40,661,000
Deferred compensation	0	0
Total Liabilities	72,346,000	40,661,000
MGE [Member]
Assets:
Exchange-traded investments	117,000	188,000
Total Assets	117,000	188,000
Liabilities:
Derivatives, net	72,329,000	42,356,000
Deferred compensation	2,010,000	1,725,000
Total Liabilities	74,339,000	44,081,000
Derivative collateral	0	3,000,000
MGE [Member] | Level 1 [Member]
Assets:
Exchange-traded investments	117,000	188,000
Total Assets	117,000	188,000
Liabilities:
Derivatives, net	(17,000)	1,695,000
Deferred compensation	0	0
Total Liabilities	(17,000)	1,695,000
MGE [Member] | Level 2 [Member]
Assets:
Exchange-traded investments	0	0
Total Assets	0	0
Liabilities:
Derivatives, net	0	0
Deferred compensation	2,010,000	1,725,000
Total Liabilities	2,010,000	1,725,000
MGE [Member] | Level 3 [Member]
Assets:
Exchange-traded investments	0	0
Total Assets	0	0
Liabilities:
Derivatives, net	72,346,000	40,661,000
Deferred compensation	0	0
Total Liabilities	$ 72,346,000	$ 40,661,000