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Securities - Additional Information (Details)
9 Months Ended 12 Months Ended
Sep. 30, 2017
USD ($)
security
Dec. 31, 2016
USD ($)
Investments, Debt and Equity Securities [Abstract]    
FHLB stock requirement, percentage of outstanding capital 3.00%  
FHLB stock requirement, percentage subject to call 3.00%  
FHLB stock requirement, percentage of outstanding borrowings 4.25%  
Schedule of Available-for-sale Securities [Line Items]    
Other-than-temporary impairment losses recognized | $ $ 0 $ 0
Federal agencies and GSEs    
Schedule of Available-for-sale Securities [Line Items]    
Number of securities with unrealized losses 18  
Number of securities in unrealized loss position for 12 months or more 9  
Mortgage-backed securities    
Schedule of Available-for-sale Securities [Line Items]    
Number of securities with unrealized losses 33  
Number of securities in unrealized loss position for 12 months or more 9  
Collateralized mortgage obligations    
Schedule of Available-for-sale Securities [Line Items]    
Number of securities with unrealized losses 1  
State and municipal securities    
Schedule of Available-for-sale Securities [Line Items]    
Number of securities with unrealized losses 18  
Number of securities in unrealized loss position for 12 months or more 10  
Corporate securities    
Schedule of Available-for-sale Securities [Line Items]    
Number of securities with unrealized losses 2