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Share-Based Compensation (Summary Of Performance Share Units Grant-Date Fair Values And Their Related Assumptions) (Details) - Performance Share Units [Member]
9 Months Ended
Sep. 30, 2021
$ / shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Grant-date fair value $ 18.08
Risk-free interest rate 0.18%
Volatility factor 67.80%
Contractual term (years) 2 years 10 months 20 days