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Investment Securities - Non-marketable Securities (Details)
 12 Months Ended
Dec. 31, 2017
USD ($)
$ / shares
shares
Feb. 21, 2018
Dec. 31, 2016
USD ($)
Schedule of Cost-method Investments [Line Items]      
Federal Home Loan Bank stock, par value (usd per share) | $ / shares $ 100    
Investments in low income housing tax credit funds $ 2,100,000   $ 2,500,000
Low income housing tax credits and other tax benefits 332,000    
Low income housing amortization expense 331,000    
Unfunded commitments for low income housing tax credit funds 546,000    
Catch-up amortization expense due to tax reduction $ 67,000    
Subsequent event      
Schedule of Cost-method Investments [Line Items]      
Federal Home Loan Bank, dividend rate percentage   7.00%  
Visa Inc. Class B common stock      
Schedule of Cost-method Investments [Line Items]      
Number of shares of securities carried at cost | shares 16,939    
Carrying value of securities carried at cost $ 0    
Fair value of Class B common stock $ 3,200,000   2,200,000
Conversion ratio for common stock 1.6483    
Other assets      
Schedule of Cost-method Investments [Line Items]      
Federal Home Loan Bank stock $ 11,100,000   $ 10,200,000