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Stockholders' Equity - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2017
Jan. 01, 2018
Dec. 31, 2016
Dec. 31, 2015
Stockholders Equity [Line Items]        
Increase remaining shares to be purchased 300,000   300,000 332,552
2016 [Member]        
Stockholders Equity [Line Items]        
Implementation of the capital conservation buffer, Percentage 0.625%      
Capital conservation buffer implementation phase-in period 4 years      
2019 [Member]        
Stockholders Equity [Line Items]        
Capital Conservation Buffer Maximum Level 2.50%      
Maximum [Member]        
Stockholders Equity [Line Items]        
Quantitative limit for trust preferred securities to be included in tier 1 capital $ 15,000,000,000      
Subsequent Event [Member]        
Stockholders Equity [Line Items]        
Available equity of BancFirst for dividend payments to the company   $ 100,800,000    
Senior Preferred Stock [Member]        
Stockholders Equity [Line Items]        
Preferred stock, shares issued 0   0  
Preferred stock, shares outstanding 0      
Cumulative Preferred Stock [Member]        
Stockholders Equity [Line Items]        
Preferred stock, shares issued 0   0  
Preferred stock, shares outstanding 0      
Dividend payable at redemption, per share $ 5.00      
Cumulative preferred stock dividend rate 10.00%