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
-SubTopic 10
-Section 15
-Paragraph 4
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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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No definition available.

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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
-Section S99
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Joint Plant Ownership (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended		12 Months Ended
Joint Plant Ownership (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	Jan. 01, 2017
Jointly Owned Utility Plant Interests [Line Items]
Assets held for sale	$ 5,117	$ 5,117		$ 14,813
Accrued capital expenditures		8,450	$ 7,091
MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Assets held for sale	5,117	5,117		$ 14,813
Accrued capital expenditures		8,450	$ 7,091
Columbia Units [Member] \| MGE [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share				22.00%	20.40%
Assets held for sale	5,100	5,100		$ 14,800
Accrued capital expenditures	$ 2,800	$ 5,100		$ 14,800