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Loans - Additional Information (Detail)
3 Months Ended 12 Months Ended
Mar. 31, 2019
USD ($)
Property
Contract
Mar. 31, 2018
USD ($)
Contract
Dec. 31, 2018
USD ($)
Contract
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Loans serviced for others $ 94,500,000   $ 92,300,000
Concentrations of loans related to a single industry 0 $ 0  
Loans classified as troubled debt restructurings 2,200,000   1,500,000
Reserves allocated to customers whose loan terms are modified in troubled debt restructurings 17,000   17,000
Loans payable in nonaccrual of interest status 271,000    
Mortgage loans in process of foreclosure amount 56,000   57,000
Other real estate real estate acquired through foreclosure 99,000   99,000
Other repossessed assets $ 15,000   $ 0
Number of properties acquired | Property 1    
Number of loans restructured | Contract 1 0  
Loans restructured, subsequently defaulted | Contract 1   0
Loans restructured, subsequently defaulted $ 200,000    
Outstanding balance of commercial loans classified under credit risk, minimum amount 300,000    
Loans listed as not rated under risk category, maximum amount 300,000    
Performing [Member]      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Loans classified as troubled debt restructurings $ 1,900,000