Fair Value of Financial Instruments (Details-2) - USD ($) $ in Thousands		Mar. 31, 2016		Dec. 31, 2015
Liabilities:
Derivative liability, collateral offset		$ 1,000		$ 1,000
Recurring [Member]
Assets:
Derivative assets, net		236	[1]	234
Total Assets		721		993
Liabilities:
Derivative liabilities, net	[1]	57,120		54,316
Deferred compensation		3,228		3,145
Total liabilities		60,348		57,461
Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		485		759
Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net		217	[1]	0
Total Assets		702		759
Liabilities:
Derivative liabilities, net	[1]	0		581
Deferred compensation		0		0
Total liabilities		0		581
Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		485		759
Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net		0	[1]	0
Total Assets		0		0
Liabilities:
Derivative liabilities, net	[1]	0		0
Deferred compensation		3,228		3,145
Total liabilities		3,228		3,145
Recurring [Member] | Level 2 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		0		0
Recurring [Member] | Level 3 [Member]
Assets:
Derivative assets, net		19	[1]	234
Total Assets		19		234
Liabilities:
Derivative liabilities, net	[1]	57,120		53,735
Deferred compensation		0		0
Total liabilities		57,120		53,735
Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		0		0
MGE [Member]
Liabilities:
Derivative liability, collateral offset		1,000		1,000
MGE [Member] | Recurring [Member]
Assets:
Derivative assets, net		236	[1]	234
Total Assets		335		382
Liabilities:
Derivative liabilities, net	[1]	57,120		54,316
Deferred compensation		3,228		3,145
Total liabilities		60,348		57,461
MGE [Member] | Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		99		148
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net		217	[1]	0
Total Assets		316		148
Liabilities:
Derivative liabilities, net	[1]	0		581
Deferred compensation		0		0
Total liabilities		0		581
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities		99		148
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net		0	[1]	0
Total Assets		0		0
Liabilities:
Derivative liabilities, net	[1]	0		0
Deferred compensation		3,228		3,145
Total liabilities		3,228		3,145
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		19	[1]	234
Total Assets		19		234
Liabilities:
Derivative liabilities, net	[1]	57,120		53,735
Deferred compensation		0		0
Total liabilities		57,120		53,735
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 $1.0 million of collateral that was posted against derivative positions with counterparties as of March 31, 2016 and December 31, 2015.