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Compensation Plans: Stock Based (Details)
$ in Millions
3 Months Ended
Mar. 31, 2021
USD ($)
shares
Mar. 31, 2021
USD ($)
shares
Mar. 31, 2020
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares available for grant | shares 3,800,000 3,800,000  
Performance Shares (PSUs)      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award Vesting Period 3 years    
Stock-based compensation expense   $ 3.2 $ 2.6
Unrecognized stock based compensation expense $ 4.5 $ 4.5  
Performance Shares (PSUs) | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Multiplier applied to PSU awards at settlement 0 0  
Performance Shares (PSUs) | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Multiplier applied to PSU awards at settlement 2 2  
Restricted Stock Units (RSUs)      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Stock-based compensation expense   $ 2.2 $ 2.6
Unrecognized stock based compensation expense $ 12.5 $ 12.5  
Number of shares represented by each RSU | shares 1 1