Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies - Additional Information (Detail)

v3.20.4
Summary of Significant Accounting Policies - Additional Information (Detail)
 12 Months Ended
Dec. 31, 2020
USD ($)
branch
Segment
shares
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Jan. 24, 2019
shares
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Number of reportable segments | Segment 1      
Accrued interest receivable on available-for-sale debt securities $ 1,200,000      
Impairment of intangible assets 0      
Goodwill impairment loss 0      
Bank-owned life insurance $ 53,894,000 $ 52,782,000    
Stock options, expiration term from date of grant 10 years      
Number of shares authorized for repurchase (percent)       5.00%
Number of shares authorized for repurchase under program (shares) | shares       1,500,000
Shares repurchased $ 2,196,000 7,362,000 $ 36,068,000  
Increase to beginning balance of allowance for credit losses 17,400,000      
Decrease to beginning balance of allowance for off balance sheet items (335,000)      
Retained earnings 114,621,000 $ 100,551,000    
Cumulative Effect Period of Adoption Adjustment | Impact of ASU 2016-13 Adoption        
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Retained earnings $ 12,200,000      
Stock Repurchase Program        
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Shares repurchased (shares) | shares 135,400      
Shares repurchased $ 2,200,000      
Minimum        
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Period of continuous service 3 years      
Maximum        
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Period of continuous service 5 years      
Split Dollar Death Benefit Agreement        
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Bank-owned life insurance $ 3,400,000      
Full Service        
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Number of branches | branch 35      
Loan Production        
Financing Receivable, Recorded Investment, Past Due [Line Items]        
Number of branches | branch 9