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Asset Retirement Obligations (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Asset Retirement Obligations [Roll Forward]    
Asset retirement obligation, beginning balance $ 28,355 $ 29,980
Liabilities incurred [1] 3,503 1,586
Accretion expense 1,366 1,574
Liabilities settled (372) (323)
Revisions in estimated cash flows [2] (1,656) (4,462)
Asset retirement obligation, ending balance 31,196 28,355
Two Creeks [Member]    
Asset Retirement Obligations [Roll Forward]    
Liabilities incurred $ 3,200  
Saratoga Wind Farm [Member]    
Asset Retirement Obligations [Roll Forward]    
Liabilities incurred   $ 1,500
[1] 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 Two Creeks. In 2019, MGE recorded an obligation of $1.5 million for the fair value of its legal liability for AROs associated with Saratoga. Construction of Saratoga was completed in February 2019.
[2] In 2019, MGE revised the AROs associated with certain wind farms based on updated estimated decommissioning costs.