Fair Value of Financial Instruments (Details-4) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		$ (53,986)	$ (64,628)	$ (72,346)
Realized and unrealized gains (losses):
Included in regulatory liabilities		484	10,642	7,718
Included in other comprehensive income		0	0	0
Included in earnings	[1]	(6,635)	5,129	(2,618)
Included in current assets		0	0	(108)
Purchases		23,052	26,382	23,726
Sales		35	(125)	(2)
Issuances		0	0	0
Settlements		(16,451)	(31,386)	(20,998)
Transfers in and/or out of Level 3		0	0	0
Ending balance		(53,501)	(53,986)	(64,628)
Total gains (losses) included in earnings attributed to the change in unrealized gains (losses) related to assets and liabilities	[1]	0	0	0
Purchased Power Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	[1]	(6,663)	5,137	(2,618)
Cost Of Gas Sold Expense [Member]
Realized and unrealized gains (losses):
Included in earnings	[1]	$ 28	$ (8)	$ 0

[1] MGE's exchange-traded derivative contracts, over-the-count er 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.