Fair Value of Financial Instruments (Details-4) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance,		$ (53,866)	$ (58,797)	$ (53,986)	$ (64,628)
Realized and unrealized gains (losses):
Included in regulatory liabilities (assets)		(2,327)	9,448	(2,208)	15,279
Included in other comprehensive income		0	0	0	0
Included in earnings	[1]	(883)	651	(2,211)	7,218
Included in current assets		0	(185)	0	(185)
Purchases		4,953	6,828	11,115	13,634
Sales		0	0	34	(60)
Issuances		0	0	0	0
Settlements		(4,071)	(7,294)	(8,938)	(20,607)
Transfers in and/or out of level 3		0	0	0	0
Ending balance,		(56,194)	(49,349)	(56,194)	(49,349)
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]	(885)	651	(2,213)	7,218
Cost Of Gas Sold Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	[1]	$ 2	$ 0	$ 2	$ 0

[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.