Fair Value of Financial Instruments (Details-4) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance,	$ (49,349)		$ (66,856)		$ (64,628)		$ (72,346)
Realized and unrealized gains (losses):
Included in regulatory liabilities (assets)	(3,752)		(1,472)		11,528		4,018
Included in other comprehensive income	0		0		0		0
Included in earnings	(1,419)		(174)		5,837		(2,034)
Included in current assets	0		(38)		(89)		(94)
Purchases	6,371		6,052		19,900		17,709
Sales	0		0		(60)		(2)
Issuances	0		0		0		0
Settlements	(4,952)		(5,840)		(25,589)		(15,579)
Transfers in and/or out of level 3	0		0		0		0
Ending balance,	(53,101)		(68,328)		(53,101)		(68,328)
Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities	0	[1]	0	[1]	0	[1]	0	[1]
Purchased Power Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	(1,411)	[1]	(174)	[1]	5,845	[1]	(2,034)	[1]
Cost Of Gas Sold Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	$ (8)	[1]	$ 0	[1]	$ (8)	[1]	$ 0	[1]

[1] MGE's exchange-traded derivative contracts, over-the-counter party transactions, ten-year 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.