Annual report pursuant to Section 13 and 15(d)

Business Combinations - Additional Information (Details)

v3.20.4
Business Combinations - Additional Information (Details)
12 Months Ended
Feb. 28, 2020
USD ($)
Branch
Nov. 05, 2019
USD ($)
Branch
shares
Apr. 02, 2019
USD ($)
Branch
office
shares
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Business Acquisition [Line Items]            
Goodwill       $ 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       $ 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      
Business acquisition, cash paid     $ 32,377,000      
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       $ 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 premises and equipment       262,000    
Business acquisition, measurement period adjustments to other assets       296,000    
Business acquisition, measurement period adjustments to other liabilities       $ 499,000    
Business acquisition, cash paid   $ 17,902,000        
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       $ 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          
Business acquisition, cash paid $ 131,571,000          
Goodwill deductible for tax purpose amortization period 15 years          
Simmons Bank | North/South Texas            
Business Acquisition [Line Items]            
Number of additional branches | Branch 5