Fair Value of Financial Instruments (Details-4) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance,		$ (51,883)	$ (56,194)	$ (53,501)	$ (53,986)
Realized and unrealized gains (losses):
Included in regulatory (assets) liabilities		1,455	(888)	3,073	(3,096)
Included in other comprehensive income		0	0	0	0
Included in earnings	[1]	(278)	(2,285)	(4,250)	(4,497)
Included in current assets		0	0	0	0
Purchases		5,814	6,364	16,751	17,497
Sales		0	0	0	0
Issuances		0	0	0	0
Settlements		(5,537)	(4,079)	(12,502)	(13,000)
Transfers in and/or out of level 3		0	0	0	0
Ending balance,		(50,429)	(57,082)	(50,429)	(57,082)
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]	(278)	(2,302)	(4,250)	(4,515)
Cost Of Gas Sold Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	[1]	$ 0	$ 17	$ 0	$ 18

[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.