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Share Based Compensation (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Stock based compensation plans        
Share-based Payment Arrangement, Noncash Expense $ 2.2 $ 2.1 $ 7.3 $ 7.9
Employee Service Share-based Compensation Not yet Recognized $ 11.3   $ 11.3  
Employees | Restricted Stock        
Stock based compensation plans        
Grants of restricted shares (in shares)     207,077  
Shares withheld for tax withholding obligation     85,466  
Non-employees, Directors | Restricted Stock        
Stock based compensation plans        
Grants of restricted shares (in shares)     23,025