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Investment Securities - Additional Information (Detail)
12 Months Ended
Dec. 31, 2017
USD ($)
Security
Dec. 31, 2016
USD ($)
Security
Dec. 31, 2015
USD ($)
Schedule of Available-for-sale Securities [Line Items]      
Federal Reserve stock owned by Company | $ $ 508,000 $ 507,000  
Federal Home Loan Bank stock (FHLB) | $ 559,000 545,000  
Securities available for sale pledged as collateral on public deposits | $ $ 75,500,000 $ 74,800,000 $ 68,800,000
Corporate Bonds [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Number of available for sale securities related to unrealized losses less than twelve months 1    
Number of available for sale securities related to unrealized losses   2  
U.S. Government Agencies [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Number of available for sale securities related to unrealized losses less than twelve months 6    
Number of available for sale securities related to unrealized losses more than twelve months 15    
Number of securities related to unrealized losses 1 1  
Number of available for sale securities related to unrealized losses   23  
GSE - Mortgage-backed Securities and CMO's [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Number of available for sale securities related to unrealized losses less than twelve months 4    
Number of available for sale securities related to unrealized losses more than twelve months 12    
Number of available for sale securities related to unrealized losses   14  
Available for sale securities | $ $ 0    
State and Political Subdivisions [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Number of available for sale securities related to unrealized losses less than twelve months 1    
Number of available for sale securities related to unrealized losses more than twelve months 7    
Number of securities related to unrealized losses 5 8  
Number of available for sale securities related to unrealized losses   7  
U.S. Treasury [Member]      
Schedule of Available-for-sale Securities [Line Items]      
Number of available for sale securities related to unrealized losses   1