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Income Tax - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Income Taxes [Line Items]        
U.S. federal corporate tax rate   35.00% 35.00% 35.00%
Previously acquired institutions amount of allocated income to bad debt deductions   $ 12,800,000    
Unrecorded deferred income tax liability   $ 2,700,000    
Bad debt reserve, description   Retained earnings of the Bank include approximately $12.8 million for which no deferred income tax liability has been recognized. This amount represents an allocation of previously acquired institutions income to bad debt deductions as of December 31, 1987 for tax purposes only. Reductions of amounts so allocated for purposes other than tax bad debt losses including redemption of bank stock or excess dividends, or loss of “bank” status would create income for tax purposes only, which would be subject to the then-current corporate income tax rate.    
Scenario, Forecast [Member]        
Income Taxes [Line Items]        
U.S. federal corporate tax rate 21.00%      
State Tax Jurisdiction [Member]        
Income Taxes [Line Items]        
Operating loss carry forwards   $ 25,200,000    
Federal Jurisdiction [Member]        
Income Taxes [Line Items]        
Operating loss carry forwards   $ 74,000    
Minimum [Member] | State Tax Jurisdiction [Member]        
Income Taxes [Line Items]        
Operating loss carry forward expiration year   2024    
Minimum [Member] | Federal Jurisdiction [Member]        
Income Taxes [Line Items]        
Operating loss carry forward expiration year   2032