Fair Value of Financial Instruments (Details-2) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Assets:
Available-for-sale securities	$ 2,554	$ 2,822
Liabilities:
Derivative liability, collateral offset	0	1,000
Recurring [Member]
Assets:
Derivative assets, net	1,527	234
Total Assets	2,027	993
Liabilities:
Derivative liabilities, net	50,808	54,316	[1]
Deferred compensation	3,039	3,145
Total Liabilities	53,847	57,461
Recurring [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	500	759
Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net	1,041	0
Total Assets	1,541	759
Liabilities:
Derivative liabilities, net	16	581	[1]
Deferred compensation	0	0
Total Liabilities	16	581
Recurring [Member] | Level 1 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	500	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	3,039	3,145
Total Liabilities	3,039	3,145
Recurring [Member] | Level 2 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	0	0
Recurring [Member] | Level 3 [Member]
Assets:
Derivative assets, net	486	234
Total Assets	486	234
Liabilities:
Derivative liabilities, net	50,792	53,735	[1]
Deferred compensation	0	0
Total Liabilities	50,792	53,735
Recurring [Member] | Level 3 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	0	0
MGE [Member]
Assets:
Available-for-sale securities	487	518
Liabilities:
Derivative liability, collateral offset	0	1,000
MGE [Member] | Recurring [Member]
Assets:
Derivative assets, net	1,527	234
Total Assets	1,670	382
Liabilities:
Derivative liabilities, net	50,808	54,316	[1]
Deferred compensation	3,039	3,145
Total Liabilities	53,847	57,461
MGE [Member] | Recurring [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	143	148
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net	1,041	0
Total Assets	1,184	148
Liabilities:
Derivative liabilities, net	16	581	[1]
Deferred compensation	0	0
Total Liabilities	16	581
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange-traded investments
Assets:
Available-for-sale securities	143	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	3,039	3,145
Total Liabilities	3,039	3,145
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	486	234
Total Assets	486	234
Liabilities:
Derivative liabilities, net	50,792	53,735	[1]
Deferred compensation	0	0
Total Liabilities	50,792	53,735
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 million of collateral that was posted against derivative positions with counterparties as of December 31, 2015.