Fair Value of Financial Instruments (Details-2) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Liabilities:
Derivative liability, collateral offset		$ 1,000
Recurring [Member]
Assets:
Derivative assets, net	$ 1,719	234
Total Assets	2,220	993
Liabilities:
Derivative liabilities, net	52,240	54,316	[1]
Deferred compensation	3,250	3,145
Total liabilities	55,490	57,461
Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	501	759
Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net	1,362	0
Total Assets	1,863	759
Liabilities:
Derivative liabilities, net	0	581	[1]
Deferred compensation	0	0
Total liabilities	0	581
Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	501	759
Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net	0	0
Total Assets	0	0
Liabilities:
Derivative liabilities, net	0	0	[1]
Deferred compensation	3,250	3,145
Total liabilities	3,250	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	357	234
Total Assets	357	234
Liabilities:
Derivative liabilities, net	52,240	53,735	[1]
Deferred compensation	0	0
Total liabilities	52,240	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
MGE [Member] | Recurring [Member]
Assets:
Derivative assets, net	1,719	234
Total Assets	1,803	382
Liabilities:
Derivative liabilities, net	52,240	54,316	[1]
Deferred compensation	3,250	3,145
Total liabilities	55,490	57,461
MGE [Member] | Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	84	148
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net	1,362	0
Total Assets	1,446	148
Liabilities:
Derivative liabilities, net	0	581	[1]
Deferred compensation	0	0
Total liabilities	0	581
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	84	148
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net	0	0
Total Assets	0	0
Liabilities:
Derivative liabilities, net	0	0	[1]
Deferred compensation	3,250	3,145
Total liabilities	3,250	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	357	234
Total Assets	357	234
Liabilities:
Derivative liabilities, net	52,240	53,735	[1]
Deferred compensation	0	0
Total liabilities	52,240	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 December 31, 2015.