Fair Value of Financial Instruments (Details-2) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Liabilities:
Derivative asset, collateral offset	$ 300		$ 200
Recurring [Member]
Assets:
Total Assets	727		792
Liabilities:
Derivatives, net	48,854	[1]	63,893	[1]
Deferred compensation	2,591		2,364
Total liabilities	51,445		66,257
Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	727		792
Recurring [Member] | Level 1 [Member]
Assets:
Total Assets	727		792
Liabilities:
Derivatives, net	(495)	[1]	(735)	[1]
Deferred compensation	0		0
Total liabilities	(495)		(735)
Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	727		792
Recurring [Member] | Level 2 [Member]
Assets:
Total Assets	0		0
Liabilities:
Derivatives, net	0	[1]	0	[1]
Deferred compensation	2,591		2,364
Total liabilities	2,591		2,364
Recurring [Member] | Level 2 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	0		0
Recurring [Member] | Level 3 [Member]
Assets:
Total Assets	0		0
Liabilities:
Derivatives, net	49,349	[1]	64,628	[1]
Deferred compensation	0		0
Total liabilities	49,349		64,628
Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	0		0
MGE [Member]
Liabilities:
Derivative asset, collateral offset	300		200
MGE [Member] | Recurring [Member]
Assets:
Total Assets	268		431
Liabilities:
Derivatives, net	48,854	[1]	63,893	[1]
Deferred compensation	2,591		2,364
Total liabilities	51,445		66,257
MGE [Member] | Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	268		431
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Total Assets	268		431
Liabilities:
Derivatives, net	(495)	[1]	(735)	[1]
Deferred compensation	0		0
Total liabilities	(495)		(735)
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	268		431
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Total Assets	0		0
Liabilities:
Derivatives, net	0	[1]	0	[1]
Deferred compensation	2,591		2,364
Total liabilities	2,591		2,364
MGE [Member] | Recurring [Member] | Level 2 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	0		0
MGE [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Total Assets	0		0
Liabilities:
Derivatives, net	49,349	[1]	64,628	[1]
Deferred compensation	0		0
Total liabilities	49,349		64,628
MGE [Member] | Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	$ 0		$ 0

[1] These amounts are shown gross and exclude $0.3 million and $0.2 million of collateral that was posted against derivative positions with counterparties as of June 30, 2014 and December 31, 2013, respectively.