Fair Value of Financial Instruments (Details-2) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Liabilities:
Derivative liability, collateral offset		$ 800	$ 2,200
Recurring [Member]
Assets:
Derivative assets, net		379	642
Total Assets		1,006	1,569
Liabilities:
Derivative liabilities, net	[1]	57,777	55,640
Deferred compensation		3,160	2,832
Total liabilities		60,937	58,472
Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		627	927
Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net		0	0
Total Assets		627	927
Liabilities:
Derivative liabilities, net	[1]	316	1,012
Deferred compensation		0	0
Total liabilities		316	1,012
Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		627	927
Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net		0	0
Total Assets		0	0
Liabilities:
Derivative liabilities, net	[1]	0	0
Deferred compensation		3,160	2,832
Total liabilities		3,160	2,832
Recurring [Member] | Level 2 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		0	0
Recurring [Member] | Level 3 [Member]
Assets:
Derivative assets, net		379	642
Total Assets		379	642
Liabilities:
Derivative liabilities, net	[1]	57,461	54,628
Deferred compensation		0	0
Total liabilities		57,461	54,628
Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		0	0
MGE [Member]
Liabilities:
Derivative liability, collateral offset		800	2,200
MGE [Member] | Recurring [Member]
Assets:
Derivative assets, net		379	642
Total Assets		501	992
Liabilities:
Derivative liabilities, net	[1]	57,777	55,640
Deferred compensation		3,160	2,832
Total liabilities		60,937	58,472
MGE [Member] | Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		122	350
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net		0	0
Total Assets		122	350
Liabilities:
Derivative liabilities, net	[1]	316	1,012
Deferred compensation		0	0
Total liabilities		316	1,012
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		122	350
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net		0	0
Total Assets		0	0
Liabilities:
Derivative liabilities, net	[1]	0	0
Deferred compensation		3,160	2,832
Total liabilities		3,160	2,832
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:
Derivative assets, net		379	642
Total Assets		379	642
Liabilities:
Derivative liabilities, net	[1]	57,461	54,628
Deferred compensation		0	0
Total liabilities		57,461	54,628
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 $0.8 million and $2.2 million of collateral that was posted against derivative positions with counterparties as of September 30, 2015 and December 31, 2014, respectively.