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Junior Subordinated Debentures - Additional Information (Detail) - USD ($)
1 Months Ended 12 Months Ended
Oct. 08, 2015
Mar. 31, 2004
Feb. 29, 2004
Dec. 31, 2020
Dec. 31, 2019
Junior Subordinated Debentures [Line Items]          
Junior subordinated notes assumed       $ 26,804,000 $ 26,804,000
BancFirst Capital Trust Two [Member] | Subordinated Debentures Subject to Mandatory Redemption [Member]          
Junior Subordinated Debentures [Line Items]          
Interest rate of securities       7.20%  
Frequency of payment       payable January 15, April 15, July 15 and October 15 of each year.  
Junior subordinated notes assumed       $ 26,800,000  
Debt instrument maturity date       Mar. 31, 2034  
BancFirst Capital Trust Two [Member] | Cumulative Preferred Stock [Member]          
Junior Subordinated Debentures [Line Items]          
Issue of securities   $ 1,000,000 $ 25,000,000    
Cumulative trust preferred securities interest rate       7.20%  
CSB Bancshares Statutory Trust I [Member]          
Junior Subordinated Debentures [Line Items]          
Business combination, acquisition of capital securities $ 5,000,000.0        
Business combination, acquisition of common securities 155,000        
CSB Bancshares Statutory Trust I [Member] | Subordinated Deferrable Interest Debentures [Member]          
Junior Subordinated Debentures [Line Items]          
Frequency of payment       payable March 15, June 15, September 15 and December 15 of each year  
Junior subordinated notes assumed $ 5,200,000        
Debt instrument maturity date Sep. 15, 2036        
CSB Bancshares Statutory Trust I [Member] | Subordinated Deferrable Interest Debentures [Member] | LIBOR [Member]          
Junior Subordinated Debentures [Line Items]          
Debt instrument, Basis point rate 1.82%