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Derivative Instruments (Details)
$ in Millions
Sep. 30, 2021
USD ($)
MWh
Derivative Instruments and Hedging Activities Disclosures [Line Items]  
Fair value of outstanding swap agreements $ 6.9
Other Current Assets  
Derivative Instruments and Hedging Activities Disclosures [Line Items]  
Fair value of outstanding swap agreements 6.1
Other Noncurrent Assets  
Derivative Instruments and Hedging Activities Disclosures [Line Items]  
Fair value of outstanding swap agreements $ 0.8
Swap  
Derivative Instruments and Hedging Activities Disclosures [Line Items]  
Notional amount of outstanding swap agreements | MWh 356,200