Fair Value of Financial Instruments (Details-4) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance,		$ (57,101)	$ (53,866)	$ (53,501)	$ (53,986)
Realized and unrealized gains (losses):
Included in regulatory (assets) liabilities		5,218	(2,327)	1,618	(2,208)
Included in other comprehensive income		0	0	0	0
Included in earnings	[1]	(1,809)	(883)	(3,972)	(2,211)
Included in current assets		0	0	0	0
Purchases		5,636	4,953	10,937	11,115
Sales		0	0	0	0
Issuances		0	0	0	0
Settlements		(3,827)	(4,071)	(6,965)	(8,904)
Transfers in and/or out of level 3		0	0	0	0
Ending balance,		(51,883)	(56,194)	(51,883)	(56,194)
Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities	[1]	0	0	0	0
Purchased Power Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	[1]	(1,809)	(885)	(3,972)	(2,213)
Cost Of Gas Sold Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	[1]	$ 0	$ 2	$ 0	$ 2

[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.