Fair Value of Financial Instruments (Details-2) (USD $)	6 Months Ended
	Jun. 30, 2011	Dec. 31, 2010
Deferred compensation interest calculation [Abstract]
U.S Treasury Bills maturity	26
Increase compounded monthly	1.00%
Minimum annual rate	7.00%
Liabilities:
Derivative collateral	$ 0	$ 500,000
MGE Energy [Member]
Assets:
Exchange-traded investments	510,000	430,000
Total Assets	510,000	430,000
Liabilities:
Derivatives, net	22,604,000	19,230,000
Deferred compensation	1,616,000	1,525,000
Total liabilities	24,220,000	20,755,000
Derivative collateral	0	500,000
MGE Energy [Member] | Fair Value Inputs Level 1 Member
Assets:
Exchange-traded investments	510,000	430,000
Total Assets	510,000	430,000
Liabilities:
Derivatives, net	(379,000)	14,000
Deferred compensation	1,616,000	1,525,000
Total liabilities	1,237,000	1,539,000
MGE Energy [Member] | Fair Value Inputs Level 2 Member
Assets:
Exchange-traded investments	0	0
Total Assets	0	0
Liabilities:
Derivatives, net	0	0
Deferred compensation	0	0
Total liabilities	0	0
MGE Energy [Member] | Fair Value Inputs Level 3 Member
Assets:
Exchange-traded investments	0	0
Total Assets	0	0
Liabilities:
Derivatives, net	22,983,000	19,216,000
Deferred compensation	0	0
Total liabilities	22,983,000	19,216,000
MGE [Member]
Assets:
Exchange-traded investments	257,000	260,000
Total Assets	257,000	260,000
Liabilities:
Derivatives, net	22,604,000	19,230,000
Deferred compensation	1,616,000	1,525,000
Total liabilities	24,220,000	20,755,000
Derivative collateral	0	500,000
MGE [Member] | Fair Value Inputs Level 1 Member
Assets:
Exchange-traded investments	257,000	260,000
Total Assets	257,000	260,000
Liabilities:
Derivatives, net	(379,000)	14,000
Deferred compensation	1,616,000	1,525,000
Total liabilities	1,237,000	1,539,000
MGE [Member] | Fair Value Inputs Level 2 Member
Assets:
Exchange-traded investments	0	0
Total Assets	0	0
Liabilities:
Derivatives, net	0	0
Deferred compensation	0	0
Total liabilities	0	0
MGE [Member] | Fair Value Inputs Level 3 Member
Assets:
Exchange-traded investments	0	0
Total Assets	0	0
Liabilities:
Derivatives, net	22,983,000	19,216,000
Deferred compensation	0	0
Total liabilities	$ 22,983,000	$ 19,216,000