Quarterly report pursuant to Section 13 or 15(d)

Business Combinations - Additional Information (Details)

v3.20.2
Business Combinations - Additional Information (Details)
3 Months Ended 9 Months Ended
Feb. 28, 2020
USD ($)
Branch
Nov. 05, 2019
USD ($)
Branch
shares
Apr. 02, 2019
USD ($)
Branch
office
shares
Sep. 30, 2020
USD ($)
Sep. 30, 2019
USD ($)
Sep. 30, 2020
USD ($)
Sep. 30, 2019
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Business Acquisition [Line Items]                  
Goodwill       $ 77,681,000   $ 77,681,000   $ 68,503,000 $ 18,253,000
First Beeville Financial Corporation                  
Business Acquisition [Line Items]                  
Business acquisition date             Apr. 02, 2019    
Business acquisition, shares issued | shares     1,579,191            
Business acquisition, cash paid     $ 32,377,000            
Business acquisition, total consideration     $ 65,900,000            
Acquired ownership interest     100.00%            
Goodwill     $ 25,848,000            
Goodwill recognized expected to be deductible for income tax purposes     0            
Acquisition expenses       0 $ 823,000 0 $ 2,500,000    
Deemed purchased credit impaired     0            
Non-credit impaired loans fair value     296,400,000            
Contractual balance     298,900,000            
Interest income     $ 2,500,000            
First Beeville Financial Corporation | North/South Texas                  
Business Acquisition [Line Items]                  
Number of additional branches | Branch     3            
Number of loan production offices | office     2            
Chandler Bancorp, Inc.                  
Business Acquisition [Line Items]                  
Business acquisition date             Nov. 05, 2019    
Business acquisition, shares issued | shares   2,100,000              
Business acquisition, cash paid   $ 17,902,000              
Business acquisition, total consideration   62,500,000              
Goodwill   22,124,000              
Goodwill recognized expected to be deductible for income tax purposes   0              
Acquisition expenses       342,000 0 1,600,000 $ 0    
Deemed purchased credit impaired   3,200,000              
Non-credit impaired loans fair value   248,800,000              
Contractual balance   253,100,000              
Interest income   $ 1,100,000              
Business acquisition, measurement period adjustments to loan discount           1,700,000      
Business acquisition, measurement period adjustments to other assets           296,000      
Business acquisition, measurement period adjustments to premises and equipment           262,000      
Business acquisition, measurement period adjustments to other liabilities       285,000   $ 499,000      
Chandler Bancorp, Inc. | North/South Texas                  
Business Acquisition [Line Items]                  
Number of additional branches | Branch   7              
Simmons Bank                  
Business Acquisition [Line Items]                  
Business acquisition date           Feb. 28, 2020      
Business acquisition, cash paid $ 131,571,000                
Goodwill 11,456,000                
Acquisition expenses       $ 0 $ 0 $ 441,000 $ 0    
Deemed purchased credit impaired 0                
Non-credit impaired loans fair value 255,500,000                
Contractual balance 260,300,000                
Interest income $ 4,800,000                
Goodwill deductible for tax purpose amortization period 15 years                
Simmons Bank | North/South Texas                  
Business Acquisition [Line Items]                  
Number of additional branches | Branch 5