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Basis of Presentation and Summary of Significant Accounting Polices - Advertising Costs (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Selling, General, and Administrative Expenses      
Basis of Presentation and Summary of Significant Accounting Policies      
Advertising expense $ 2.6 $ 4.2 $ 4.2