Fair Value of Financial Instruments (Details-4) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance,	$ (58,797)		$ (69,598)		$ (64,628)		$ (72,346)
Realized and unrealized gains (losses):
Included in regulatory liabilities (assets)	9,448		2,743		15,279		5,490
Included in other comprehensive income	0		0		0		0
Included in earnings	651		(44)		7,218		(1,351)
Included in current assets	(185)		(123)		(185)		(123)
Purchases	6,828		6,162		13,634		11,724
Sales	0		0		(60)		(2)
Issuances	0		0		0		0
Settlements	(7,294)		(5,996)		(20,607)		(10,248)
Transfers in and/or out of level 3	0		0		0		0
Ending balance,	(49,349)		(66,856)		(49,349)		(66,856)
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	$ 651	[1]	$ (44)	[1]	$ 7,218	[1]	$ (1,351)	[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 with a corresponding regulatory asset or liability.