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Commitments and Contingencies - Licensor Expense Reimbursement (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Licensor Expense Reimbursement      
Commitments and contingencies      
Expense for prosecution and maintenance of patent rights $ 13.1 $ 13.5 $ 14.2