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Financial Instruments and Risk Management - Credit and Liquidity Risk (Details) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Financial Instruments [Abstract]    
Percent of gross accounts receivable over 90 days past due (less than in 2019) 1.00% 2.00%
Allowance for doubtful accounts $ 5.0 $ 4.2