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Allowance for Loan Losses - Additional Information (Detail) - USD ($)
3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Allowance For Loan Losses [Line Items]    
Accruing Loans 90 or More Days Past Due $ 0 $ 0
Real Estate - Residential [Member]    
Allowance For Loan Losses [Line Items]    
Foreclosed residential real estate, loan amount 211,000 371,000
Real estate in process of foreclosure, loan amount 161,000 161,000
Accruing Loans 90 or More Days Past Due $ 0 $ 0