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Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Asset Retirement Obligations [Roll Forward]    
Asset retirement obligation, beginning balance $ 31,196 $ 28,355
Liabilities incurred [1] 8,589 3,503
Accretion expense 1,526 1,366
Liabilities settled (354) (372)
Revisions in estimated cash flows [2] 5,623 (1,656)
Asset retirement obligation, ending balance 46,580 31,196
Two Creeks [Member]    
Asset Retirement Obligations [Roll Forward]    
Liabilities incurred   3,200
Badger Hollow [Member]    
Asset Retirement Obligations [Roll Forward]    
Liabilities incurred $ 4,900 $ 3,400
[1] In 2021, MGE recorded an obligation of $4.9 million and $3.4 million, respectively, for the fair value of its legal liability for AROs associated with Badger Hollow I and other completed renewable projects. In 2020, MGE recorded an obligation of $3.2 million for the fair value of its legal liability for AROs associated with Two Creeks. See Footnote 6 for additional information on Badger Hollow I and Two Creeks.
[2] In 2021, MGE revised the AROs associated with certain Columbia assets.