Amount of assets held-for-sale that are not part of a disposal group, expected to be sold within a year or the normal operating cycle, if longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
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-Section 15
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Future cash outflow to pay for purchases of fixed assets that have occurred.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The proportionate share of interest (percent) in a jointly owned utility plant.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 360
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Joint Plant Ownership (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
Joint Plant Ownership (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Jan. 01, 2018
Jointly Owned Utility Plant Interests [Line Items]
Assets held for sale	$ 1,383		$ 8,817
Accrued capital expenditures	4,706	$ 6,804
MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Assets held for sale	1,383		$ 8,817
Accrued capital expenditures	4,706	$ 6,804
Columbia Units [Member] \| MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share			20.40%	19.40%
Assets held for sale	1,400		$ 8,800
Accrued capital expenditures	$ 1,400		$ 8,800