Fair Value of Financial Instruments (Details-2) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Liabilities:
Derivative asset, collateral offset	$ 0	$ 200
Recurring [Member]
Assets:
Derivative assets, net	2,267	1,787	[1]
Total Assets	3,153	2,579
Liabilities:
Derivative liabilities, net	54,951	65,680
Deferred compensation	2,705	2,364
Total liabilities	57,656	68,044
Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	886	792
Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net	417	735	[1]
Total Assets	1,303	1,527
Liabilities:
Derivative liabilities, net	0	0
Deferred compensation	0	0
Total liabilities	0	0
Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	886	792
Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net	0	0	[1]
Total Assets	0	0
Liabilities:
Derivative liabilities, net	0	0
Deferred compensation	2,705	2,364
Total liabilities	2,705	2,364
Recurring [Member] | Level 2 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	0	0
Recurring [Member] | Level 3 [Member]
Assets:
Derivative assets, net	1,850	1,052	[1]
Total Assets	1,850	1,052
Liabilities:
Derivative liabilities, net	54,951	65,680
Deferred compensation	0	0
Total liabilities	54,951	65,680
Recurring [Member] | Level 3 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	0	0
MGE [Member]
Liabilities:
Derivative asset, collateral offset	0	200
MGE [Member] | Recurring [Member]
Assets:
Derivative assets, net	2,267	1,787	[1]
Total Assets	2,608	2,218
Liabilities:
Derivative liabilities, net	54,951	65,680
Deferred compensation	2,705	2,364
Total liabilities	57,656	68,044
MGE [Member] | Recurring [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	341	431
MGE [Member] | Recurring [Member] | Level 1 [Member]
Assets:
Derivative assets, net	417	735	[1]
Total Assets	758	1,166
Liabilities:
Derivative liabilities, net	0	0
Deferred compensation	0	0
Total liabilities	0	0
MGE [Member] | Recurring [Member] | Level 1 [Member] | Exchange Traded [Member]
Assets:
Available-for-sale securities	341	431
MGE [Member] | Recurring [Member] | Level 2 [Member]
Assets:
Derivative assets, net	0	0	[1]
Total Assets	0	0
Liabilities:
Derivative liabilities, net	0	0
Deferred compensation	2,705	2,364
Total liabilities	2,705	2,364
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	1,850	1,052	[1]
Total Assets	1,850	1,052
Liabilities:
Derivative liabilities, net	54,951	65,680
Deferred compensation	0	0
Total liabilities	54,951	65,680
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 $0.2 million of collateral that was posted against derivative positions with counterparties as of December 31, 2013.