Fair Value of Financial Instruments (Details-2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Assets:
Available-for-sale securities	$ 2,729		$ 2,365
Derivative asset, collateral offset			200
Liabilities:
Derivative liability, collateral offset	2,200
Recurring [Member]
Assets:
Derivative assets, net	642		1,787	[1]
Total Assets	1,569		2,579
Liabilities:
Derivative liabilities, net	55,640	[1]	65,680
Deferred compensation	2,832		2,364
Total Liabilities	58,472		68,044
Recurring [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	927		792
Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net	0		735	[1]
Total Assets	927		1,527
Liabilities:
Derivative liabilities, net	1,012	[1]	0
Deferred compensation	0		0
Total Liabilities	1,012		0
Recurring [Member] | Level 1 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	927		792
Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net	0		0	[1]
Total Assets	0		0
Liabilities:
Derivative liabilities, net	0	[1]	0
Deferred compensation	2,832		2,364
Total Liabilities	2,832		2,364
Recurring [Member] | Level 2 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	0		0
Recurring [Member] | Level 3 [Member]
Assets:
Derivative assets, net	642		1,052	[1]
Total Assets	642		1,052
Liabilities:
Derivative liabilities, net	54,628	[1]	65,680
Deferred compensation	0		0
Total Liabilities	54,628		65,680
Recurring [Member] | Level 3 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	0		0
MGE [Member]
Assets:
Available-for-sale securities	729		811
Derivative asset, collateral offset			200
Liabilities:
Derivative liability, collateral offset	2,200
MGE [Member] | Recurring [Member]
Assets:
Derivative assets, net	642		1,787	[1]
Total Assets	992		2,218
Liabilities:
Derivative liabilities, net	55,640	[1]	65,680
Deferred compensation	2,832		2,364
Total Liabilities	58,472		68,044
MGE [Member] | Recurring [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	350		431
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net	0		735	[1]
Total Assets	350		1,166
Liabilities:
Derivative liabilities, net	1,012	[1]	0
Deferred compensation	0		0
Total Liabilities	1,012		0
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	350		431
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net	0		0	[1]
Total Assets	0		0
Liabilities:
Derivative liabilities, net	0	[1]	0
Deferred compensation	2,832		2,364
Total Liabilities	2,832		2,364
MGE [Member] | Recurring [Member] | Level 2 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	0		0
MGE [Member] | Recurring [Member] | Level 3 [Member]
Assets:
Derivative assets, net	642		1,052	[1]
Total Assets	642		1,052
Liabilities:
Derivative liabilities, net	54,628	[1]	65,680
Deferred compensation	0		0
Total Liabilities	54,628		65,680
MGE [Member] | Recurring [Member] | Level 3 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	$ 0		$ 0

[1] These amounts are shown gross and exclude $2.2 and $0.2 million of collateral that was posted against derivative positions with counterparties as of December 31, 2014 and 2013, respectively.