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Revenues (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Disaggregation of Revenue [Line Items]    
Earned rewards, expiration period 90 days  
Trade accounts receivable $ 168.8 $ 172.9
Receivables related to contracts with customers    
Disaggregation of Revenue [Line Items]    
Trade accounts receivable $ 88.3 $ 96.0
Petroleum product sales, rack sales    
Disaggregation of Revenue [Line Items]    
Collection period 10 days  
Renewable Identification Numbers (RINs) sales    
Disaggregation of Revenue [Line Items]    
Collection period 5 days  
Minimum | Petroleum product sales (at retail)    
Disaggregation of Revenue [Line Items]    
Collection period 2 days  
Maximum | Petroleum product sales (at retail)    
Disaggregation of Revenue [Line Items]    
Collection period 7 days