Fair Value of Financial Instruments (Details-4) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance,		$ (53,501)	$ (53,986)
Realized and unrealized gains (losses):
Included in regulatory (assets) liabilities		(3,600)	119
Included in other comprehensive income		0	0
Included in earnings	[1]	(2,163)	(1,328)
Included in current assets		0	0
Purchases		5,301	6,162
Sales		0	0
Issuances		0	0
Settlements		(3,138)	(4,833)
Transfers in and/or out of level 3		0	0
Ending balance,		(57,101)	(53,866)
Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities	[1]	0	0
Purchased Power Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	[1]	$ (2,163)	$ (1,328)

[1] MGE's exchange-traded derivative contracts, over-the-counter party transactions, purchased power agreement, and FTRs are subject to regulatory deferral. These derivatives are therefore marked to fair value and are offset in the financial statements with a corresponding regulatory asset or liability.