Common Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended								12 Months Ended
	Dec. 20, 2013	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Class of Stock [Line Items]
Stock split declared December 20, 2013, ratio (3:2)	1.5
Common stock dividends declared										$ 37,107	[1]	$ 35,951	[2]	$ 35,026	[3]
Common stock dividends declared (in dollars per share)		$ 0.272	$ 0.272	$ 0.263	$ 0.263	$ 0.263	$ 0.263	$ 0.255	$ 0.255	$ 1.07		$ 1.04		$ 1.01
Shares of preferred stock		0				0				0		0		1,175,000
Par value of preferred stock (in dollars per share)														$ 25
Preferred stock, shares issued		0				0				0		0		0
Preferred stock, shares outstanding		0				0				0		0		0
MGE [Member]
Class of Stock [Line Items]
Cash dividends paid to parent by MGE										$ 25,000		$ 20,404		$ 26,648

[1] $1.07 per share

[2] $1.04 per share

[3] $1.01 per share