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Significant Risks and Uncertainties (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Concentration Risk [Line Items]      
Reduction of maximum loss due to counterparty credit risk by master netting provision $ 44.2    
Allowance for doubtful accounts $ 0.1 $ 0.0  
Commercial Relationship [Member] | Consolidated Revenues [Member]      
Concentration Risk [Line Items]      
Percentage of consolidated revenues 11.00% 12.00% 15.00%
Maximum [Member]      
Concentration Risk [Line Items]      
Potential loss attributable to individual counterparties $ 17.5    
Minimum [Member]      
Concentration Risk [Line Items]      
Potential loss attributable to individual counterparties $ 0.8