Noncontrolling Interest (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
MGE [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interest on balance sheet	$ 125,689		$ 118,963
Net income attributable to noncontrolling interest, net of tax	26,310		27,438		24,489
MGE Transco [Member]
Noncontrolling Interest [Line Items]
Noncontrolling interest on balance sheet	22,397	[1]	19,998	[1]
Net income attributable to noncontrolling interest, net of tax	2,484	[1]	2,408	[1]	2,146	[1]
MGE Power [Member]
Noncontrolling Interest [Line Items]
Ownership percentage by parent	100.00%
MGE Power West Campus [Member]
Noncontrolling Interest [Line Items]
Ownership percentage by parent	100.00%
Noncontrolling interest on balance sheet	30,755	[2]	29,089	[2]
Net income attributable to noncontrolling interest, net of tax	7,666	[2]	7,657	[2]	7,506	[2]
MGE Power Elm Road [Member]
Noncontrolling Interest [Line Items]
Ownership percentage by parent	100.00%
Noncontrolling interest on balance sheet	72,537	[2]	69,876	[2]
Net income attributable to noncontrolling interest, net of tax	$ 16,160	[2]	$ 17,373	[2]	$ 14,837	[2]

[1] At December 31,2014, MGE is the majority owner, and MGE Energy is the minority owner, of MGE Transco. MGE Energy's proportionate share of the equity and net income of MGE Transco is classified within the MGE financial statements as noncontrolling interest.

[2] MGE Power Elm Road and MGE Power West Campus are not subsidiaries of MGE; however, they have been consolidated in the consolidated financial statements of MGE (see Footnote 2). MGE Power Elm Road and MGE Power West Campus are100% owned by MGE Power, and MGE Power is 100% owned by MGE Energy. MGE Energy's proportionate share of the equity and net income (through its wholly owned subsidiary MGE Power) of MGE Power Elm Road and MGE Power West Campus is classified within the MGE financial statements as noncontrolling interest.