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OTHER BORROWED FUNDS - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Jun. 27, 2016
Debt Instrument [Line Items]      
Additional line of credit available with FHLB $ 401,000,000    
Outstanding balance on secured line of credit 0 $ 1,000,000  
Junior subordinated debt $ 5,792,000 $ 3,609,000  
Revolving Line of Credit | The Independent Bankers Bank (TIB)      
Debt Instrument [Line Items]      
Revolving line of credit amount borrowed     $ 20,000,000
Revolving line of credit maturity date Jun. 27, 2018    
Unsecured Debt      
Debt Instrument [Line Items]      
Total lines of credit, available amount $ 55,000,000    
Total lines of credit, outstanding balances 0    
Loan Portfolio      
Debt Instrument [Line Items]      
Collateral agreement with the FHLB 499,000,000    
Investment Securities      
Debt Instrument [Line Items]      
Collateral agreement with the FHLB $ 72,600,000