Fair Value of Financial Instruments (Details-3) - US Treasury Bills [Member]	9 Months Ended
Sep. 30, 2022
Deferred compensation plan [Abstract]
Investment interest calculation, investment maturity period (26 weeks)	182 days
Investment interest calculation, monthly compounding rate	1.00%
Investment interest calculation, minimum annual rate compounded monthly	7.00%

Minimum annual rate compounded monthly used in deferred compensation interest calculation.

No definition available.

Name:	mgee_DeferredCompensationArrangementWithIndividualInvestmentInterestCalculationMinimumAnnualRateCompoundedMonthly
Namespace Prefix:	mgee_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration