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Basis of Accounting and Consolidation Basis of Accounting and Consolidation (Stock Plans) (Details) - shares
3 Months Ended 12 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Maximum number of shares to be issued in stock incentive plan (in shares) 149,983    
Employee Stock Purchase Plan [Abstract]      
Employee Discount for Employee Stock Purchase Plan 5.00%    
Employee Stock Purchase Plan, Number Of Shares Authorized 600,000    
Stock Issued During Period, Shares, Employee Stock Purchase Plans 782 0  
Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock awarded in SI plan (in shares) 13,250    
Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock awarded in SI plan (in shares) 15,540   28,700