Quarterly report pursuant to Section 13 or 15(d)

Allowance for Loan and Lease Losses - Additional Information (Details)

v3.20.2
Allowance for Loan and Lease Losses - Additional Information (Details)
3 Months Ended 4 Months Ended 9 Months Ended 12 Months Ended
Feb. 28, 2020
USD ($)
Apr. 02, 2019
USD ($)
Sep. 30, 2020
USD ($)
Loan
Sep. 30, 2019
USD ($)
Loan
Jun. 30, 2020
USD ($)
Loan
Sep. 30, 2020
USD ($)
Loan
Contract
Sep. 30, 2019
USD ($)
Loan
Dec. 31, 2019
USD ($)
Loan
Contract
Nov. 05, 2019
USD ($)
Financing Receivable Recorded Investment Past Due [Line Items]                  
Provision for loan losses     $ 2,831,000 $ 900,000   $ 6,840,000 $ 2,081,000    
Recorded investment, 90 days past due and still accruing               $ 2,000  
Non-accrual loans, Past due     $ 8,730,000     $ 8,730,000   $ 6,459,000  
Number of qualified loans | Contract           19   10  
Number of restructured loans, defaulted | Loan     0 0   0 0    
Covid-19                  
Financing Receivable Recorded Investment Past Due [Line Items]                  
Description of Loan modifications           Loan modifications made between March 1, 2020 and the earlier of i) December 30, 2020 or ii) 60 days after the President declares a termination of the COVID-19 national emergency are eligible for this relief if the related loans were not more than 30 days past due as of December 31, 2019.      
Number of qualified loans | Loan         1,216        
Loans, deferrals days     90 days   90 days        
Loans, interest only payment period         90 days        
Unpaid principal balance         $ 520,600,000        
Loans resumed for regularly scheduled payments     $ 414,600,000     $ 414,600,000      
Payments remaining in deferral     $ 106,000,000     $ 106,000,000      
Financing Receivables, Past Due Greater Than 90 Days or More and Still Accruing                  
Financing Receivable Recorded Investment Past Due [Line Items]                  
Recorded investment, 90 days past due and still accruing number of loans | Loan     0     0   1  
Non-accrual loans, Past due     $ 2,100,000     $ 2,100,000   $ 2,600,000  
Financing Receivables, 30 to 59 Days Past Due                  
Financing Receivable Recorded Investment Past Due [Line Items]                  
Non-accrual loans, Past due     730,000     730,000   308,000  
Financing Receivables, 60 to 89 Days Past Due                  
Financing Receivable Recorded Investment Past Due [Line Items]                  
Non-accrual loans, Past due     370,000     370,000   $ 1,200,000  
Second 90 Day Deferral Period | Covid-19                  
Financing Receivable Recorded Investment Past Due [Line Items]                  
Payments requested for deferral periods     24,800,000     24,800,000      
Third 90 Day Deferral Period | Covid-19                  
Financing Receivable Recorded Investment Past Due [Line Items]                  
Payments requested for deferral periods     7,000,000.0     7,000,000.0      
Paycheck Protection Loans                  
Financing Receivable Recorded Investment Past Due [Line Items]                  
Provision for loan losses           $ 0      
Percentage Reserve           0.00%      
Beeville                  
Financing Receivable Recorded Investment Past Due [Line Items]                  
Business combination loan in acquiree, amount   $ 298,900,000              
Business combination loan In acquiree, fair value   296,400,000              
Business combination loan in acquiree, discount   2,500,000              
Contractual balance   298,900,000              
Non-credit impaired loans fair value   $ 296,400,000              
Citizens                  
Financing Receivable Recorded Investment Past Due [Line Items]                  
Business combination loan in acquiree, discount                 $ 1,100,000
Contractual balance                 253,100,000
Non-credit impaired loans fair value                 248,800,000
Purchased credit impaired loans fair value                 $ 3,200,000
Citizens | Purchased Credit Impaired Loans                  
Financing Receivable Recorded Investment Past Due [Line Items]                  
Impaired loans     576,000     $ 576,000      
Simmons Bank                  
Financing Receivable Recorded Investment Past Due [Line Items]                  
Business combination loan in acquiree, amount $ 260,300,000                
Business combination loan In acquiree, fair value 255,500,000                
Business combination loan in acquiree, discount 4,800,000                
Contractual balance 260,300,000                
Non-credit impaired loans fair value $ 255,500,000                
Beeville or Simmons | Purchased Credit Impaired Loans                  
Financing Receivable Recorded Investment Past Due [Line Items]                  
Impaired loans     $ 0     $ 0