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Intangible Assets - Narrative (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Additional disclosures      
Amortization expense $ 5.2 $ 5.2 $ 6.9
Anticipated annual amortization expense for the next five years      
2020 5.0    
2021 5.0    
2022 5.0    
2023 2.3    
2024 $ 2.3