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Significant Accounting Policies - Advertising Costs (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Selling and promotional      
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]      
Advertising expenses $ 40.9 $ 37.4 $ 37.7