Fair Value of Financial Instruments (Details-2) - USD ($) $ in Thousands		Dec. 31, 2015	Dec. 31, 2014
Assets:
Available-for-sale securities		$ 2,822	$ 2,729
Liabilities:
Derivative liability, collateral offset		1,000	2,200
Recurring [Member]
Assets:
Derivative assets, net		234	642
Total Assets		993	1,569
Liabilities:
Derivative liabilities, net	[1]	54,316	55,640
Deferred compensation		3,145	2,832
Total Liabilities		57,461	58,472
Recurring [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		759	927
Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net		0	0
Total Assets		759	927
Liabilities:
Derivative liabilities, net	[1]	581	1,012
Deferred compensation		0	0
Total Liabilities		581	1,012
Recurring [Member] | Level 1 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		759	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		3,145	2,832
Total Liabilities		3,145	2,832
Recurring [Member] | Level 2 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		0	0
Recurring [Member] | Level 3 [Member]
Assets:
Derivative assets, net		234	642
Total Assets		234	642
Liabilities:
Derivative liabilities, net	[1]	53,735	54,628
Deferred compensation		0	0
Total Liabilities		53,735	54,628
Recurring [Member] | Level 3 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		0	0
MGE [Member]
Assets:
Available-for-sale securities		518	729
Liabilities:
Derivative liability, collateral offset		1,000	2,200
MGE [Member] | Recurring [Member]
Assets:
Derivative assets, net		234	642
Total Assets		382	992
Liabilities:
Derivative liabilities, net	[1]	54,316	55,640
Deferred compensation		3,145	2,832
Total Liabilities		57,461	58,472
MGE [Member] | Recurring [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		148	350
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net		0	0
Total Assets		148	350
Liabilities:
Derivative liabilities, net	[1]	581	1,012
Deferred compensation		0	0
Total Liabilities		581	1,012
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities		148	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		3,145	2,832
Total Liabilities		3,145	2,832
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		234	642
Total Assets		234	642
Liabilities:
Derivative liabilities, net	[1]	53,735	54,628
Deferred compensation		0	0
Total Liabilities		53,735	54,628
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 $1.0 and $2.2 million of collateral that was posted against derivative positions with counterparties as of December 31, 2015 and 2014, respectively.