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Share-Based Compensation (Summary of Share-Based Compensation Expense Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Director      
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]      
Compensation expense $ 0.1 $ 0.2 $ 0.3