Fair Value of Financial Instruments (Details-2) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Liabilities:
Derivative liability, collateral offset	$ 600		$ 2,200
Recurring [Member]
Assets:
Derivative assets, net	38		642
Total Assets	824		1,569
Liabilities:
Derivative liabilities, net	54,004	[1]	55,640	[1]
Deferred compensation	2,958		2,832
Total liabilities	56,962		58,472
Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	786		927
Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net	0		0
Total Assets	786		927
Liabilities:
Derivative liabilities, net	100	[1]	1,012	[1]
Deferred compensation	0		0
Total liabilities	100		1,012
Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	786		927
Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net	0		0
Total Assets	0		0
Liabilities:
Derivative liabilities, net	0	[1]	0	[1]
Deferred compensation	2,958		2,832
Total liabilities	2,958		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	38		642
Total Assets	38		642
Liabilities:
Derivative liabilities, net	53,904	[1]	54,628	[1]
Deferred compensation	0		0
Total liabilities	53,904		54,628
Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	0		0
MGE [Member]
Liabilities:
Derivative liability, collateral offset	600		2,200
MGE [Member] | Recurring [Member]
Assets:
Derivative assets, net	38		642
Total Assets	252		992
Liabilities:
Derivative liabilities, net	54,004	[1]	55,640	[1]
Deferred compensation	2,958		2,832
Total liabilities	56,962		58,472
MGE [Member] | Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	214		350
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net	0		0
Total Assets	214		350
Liabilities:
Derivative liabilities, net	100	[1]	1,012	[1]
Deferred compensation	0		0
Total liabilities	100		1,012
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	214		350
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net	0		0
Total Assets	0		0
Liabilities:
Derivative liabilities, net	0	[1]	0	[1]
Deferred compensation	2,958		2,832
Total liabilities	2,958		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	38		642
Total Assets	38		642
Liabilities:
Derivative liabilities, net	53,904	[1]	54,628	[1]
Deferred compensation	0		0
Total liabilities	53,904		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 $0.6 and $2.2 million of collateral that was posted against derivative positions with counterparties as of March 31, 2014 and December 31, 2014, respectively.