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Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Schedule Of Summary Of Significant Accounting Policies [Line Items]      
Reserve requirements $ 0 $ 0  
Securities held for trading purposes 0 0  
Mortgage loans held for sale 6,990,000 2,086,000  
Outstanding loans sold to government agencies $ 118,818,000 $ 139,303,000  
Period for appraises of property 12 months 12 months  
Other investments $ 9,735,000 $ 12,323,000  
Income tax interest or penalties 0 0 $ 0
Accrued liability for interest or penalty payments 0 0 0
Tax effect for unrealized gains (losses) on investment securities 770,000 (278,000) (520,000)
Tax effect on reclassification adjustment in net income 0 0 $ 0
Right-of-use asset 4,600,000    
Lease liability 4,600,000    
ASU 2016-13 | Pro Forma      
Schedule Of Summary Of Significant Accounting Policies [Line Items]      
Estimate of increase in allowance for loan losses expected to be reclassified from purchase discount for acquired impaired loans $ 1,200,000    
Servicing Contracts      
Schedule Of Summary Of Significant Accounting Policies [Line Items]      
Amortization of intangibles 10 years    
Nonrecurring      
Schedule Of Summary Of Significant Accounting Policies [Line Items]      
Foreclosed assets and ORE $ 4,156,000 1,558,000  
Minimum      
Schedule Of Summary Of Significant Accounting Policies [Line Items]      
Estimated useful lives of the individual assets 3 years    
Minimum | ASU 2016-13 | Pro Forma      
Schedule Of Summary Of Significant Accounting Policies [Line Items]      
Estimate of increase in allowance for loan losses expected to be reclassified from purchase discount for acquired impaired loans (percent) 30.00%    
Minimum | Core Deposits      
Schedule Of Summary Of Significant Accounting Policies [Line Items]      
Amortization of intangibles 9 years    
Maximum      
Schedule Of Summary Of Significant Accounting Policies [Line Items]      
Estimated useful lives of the individual assets 40 years    
Maximum | ASU 2016-13 | Pro Forma      
Schedule Of Summary Of Significant Accounting Policies [Line Items]      
Estimate of increase in allowance for loan losses expected to be reclassified from purchase discount for acquired impaired loans (percent) 40.00%    
Maximum | Core Deposits      
Schedule Of Summary Of Significant Accounting Policies [Line Items]      
Amortization of intangibles 15 years    
U S Government Agencies      
Schedule Of Summary Of Significant Accounting Policies [Line Items]      
Outstanding loans sold to government agencies $ 118,818,000 $ 139,303,000