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Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Asset Retirement Obligations [Roll Forward]    
Asset retirement obligation, beginning balance $ 26,738 $ 26,886
Liabilities incurred 1,943 [1] 145
Accretion expense 1,415 1,359
Liabilities settled (175) (1,789) [2]
Revisions in estimated cash flows 59 137
Asset retirement obligation, ending balance 29,980 26,738
Blount Asbestos Removal [Member]    
Asset Retirement Obligations [Roll Forward]    
Liabilities settled   $ (1,600)
Forward Wind [Member]    
Asset Retirement Obligations [Roll Forward]    
Liabilities incurred $ 1,600  
[1]
In 2018, MGE recorded an obligation of $1.6 million for the fair value of its legal liability for AROs associated with Forward Wind. See Footnote 5 for additional information on the purchase of Forward Wind.
[2]
In 2017, MGE removed a stack at Blount resulting in a $1.6 million settlement .