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Trade Accounts Receivable (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Dec. 31, 2018
Trade Accounts Receivable        
Allowance for doubtful accounts   $ 1.8   $ 1.7
Bad debt expense   0.3    
Allowance for doubtful accounts receivable, write-off   0.2    
Increase in allowance for doubtful accounts $ 0.5 $ 0.1 $ 0.9