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Stock-Based Compensation Plans - Plan Administration (Details) - 2009 Equity Compensation Plan
12 Months Ended
Dec. 31, 2020
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Number of shares available for grant (in shares) 247,000
Director  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Share-based compensation plan maximum share grants per year (in shares) 125,000
Share-based Payment Arrangement, Nonemployee | Director  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Share-based compensation plan maximum share grants per year (in shares) 20,000