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Summary of Significant Accounting Policies - Narrative - Research and Development (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Company      
Research and Development Arrangement, Contract to Perform for Others [Line Items]      
Research and development expenses $ 55.8 $ 65.1 $ 46.7
Customers      
Research and Development Arrangement, Contract to Perform for Others [Line Items]      
Research and development expenses $ 628.7 $ 680.5 $ 591.6