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Securities - Scheduled Maturities of Securities AFS Other than Mortgage Backed Securities and the Related Weighted Average Yield (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Schedule Of Available For Sale Securities [Line Items]    
Amortized cost, one through five years $ 499  
Amortized cost, five through ten years 19,000  
Amortized cost, total $ 19,499  
Weighted average yield, one through five years 1.03% 0.90%
Weighted average yield, five through ten years 5.24%  
Weighted average yield, total 5.13% 0.90%
Estimated fair value, one through five years $ 493 $ 297
Estimated fair value, five through ten years 19,000  
Estimated fair value, total 19,493 297
U.S. Treasury Securities    
Schedule Of Available For Sale Securities [Line Items]    
Amortized cost, one through five years 499 300
Amortized cost, total 499 300
Estimated fair value, one through five years 493 297
Estimated fair value, total 493 $ 297
Corporate Bonds    
Schedule Of Available For Sale Securities [Line Items]    
Amortized cost, five through ten years 19,000  
Amortized cost, total 19,000  
Estimated fair value, five through ten years 19,000  
Estimated fair value, total $ 19,000