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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-URI http://asc.fasb.org/extlink&oid=6525746

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Common Equity (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	0 Months Ended	3 Months Ended								12 Months Ended
	Dec. 20, 2013	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Class of Stock [Line Items]
Stock split declared December 20, 2013, ratio (3:2)	1.5
Common stock dividends declared										$ 38,429us-gaap_DividendsCommonStockCash	$ 37,107us-gaap_DividendsCommonStockCash	$ 35,951us-gaap_DividendsCommonStockCash
Common stock dividends declared (in dollars per share)		$ 0.283	$ 0.283	$ 0.272	$ 0.272	$ 0.272	$ 0.272	$ 0.263	$ 0.263	$ 1.11	$ 1.07	$ 1.04
MGE [Member]
Class of Stock [Line Items]
Cash dividends paid to parent by MGE										$ 26,500	$ 25,000	$ 20,404