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Share-Based Payments - Employee Share Purchase Plan (Details) - USD ($)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Stock Issued During Period, Shares, Employee Stock Purchase Plans 20,000    
Proceeds from common stock issued pursuant to Employee Share Purchase Plan $ 597,000 $ 0 $ 0
Employee Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized 2,100,000    
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date 15.00%    
Share-based Compensation Arrangement by Share-based Payment Award, Maximum Value of Share Per Employee $ 25,000    
Share-based Compensation Arrangement by Share-based Payment Award, Percentage of Outstanding Stock Maximum 0.10%    
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized 206,600    
Stock Issued During Period, Shares, Employee Stock Purchase Plans 20,178    
Proceeds from common stock issued pursuant to Employee Share Purchase Plan $ 597,000    
Allocated Share-based Compensation Expense $ 144,000    
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant 2,000,000    
Measurement Input, Price Volatility [Member] | Employee Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate 21.00%    
Measurement Input, Expected Dividend Rate [Member] | Employee Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate 2.50%    
Measurement Input, Expected Term [Member] | Employee Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term 6 months    
Measurement Input, Risk Free Interest Rate [Member] | Employee Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate 2.00%