Fair Value of Financial Instruments (Details-4) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance,	$ (64,628)		$ (72,346)
Realized and unrealized gains (losses):
Included in regulatory liabilities (assets)	5,831		2,748
Included in other comprehensive income	0		0
Included in earnings	6,634	[1]	(1,148)	[1]
Included in current assets	(53)		0
Purchases	6,859		5,562
Sales	(60)		(3)
Issuances	0		0
Settlements	(13,380)		(4,411)
Transfers in and/or out of level 3	0		0
Ending balance,	(58,797)		(69,598)
Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities	0	[1]	0	[1]
Purchased Power Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	$ 6,634	[1]	$ (1,148)	[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.