Stock-Based Compensation - Additional Information (Detail) - shares	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Deferred board fees percentage for stock units accumulation	100.00%
Nonqualified Incentive Stock Option Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period in years	7 years
Nonqualified Incentive Stock Option Plan [Member] | Stock Option [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares to be issued under incentive stock option plan	6,400,000
Shares for future grants	310,470
Stock option plan termination date	Dec. 31, 2019
Option exercisable rate	25.00%
Option exercisable period	4 years
Options expire period	15 years
Share based compensation options exercisable period	2025
Vesting period in years, start	4 years
Options vest and exercisable Description	The options vest and are exercisable beginning four years from the date of grant at the rate of 25% per year for four years. Options expire at the end of fifteen years from the date of grant
Nonqualified Incentive Stock Option Plan [Member] | Stock Option [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock price percentage to fair value at grant date	100.00%
Non-Employee Directors Stock Option Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares to be issued under incentive stock option plan	520,000
Shares for future grants	50,000
Option exercisable rate	25.00%
Option exercisable period	1 year
Options expire period	15 years
Share based compensation options exercisable period	2022
Options vest and exercisable Description	The options vest and are exercisable beginning one year from the date of grant at the rate of 25% per year for four years
Number of options granted for non-employee director	10,000
Vesting period in years	4 years
Non-Employee Directors Stock Option Plan [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock price percentage to fair value at grant date	100.00%
Banc First Deferred Stock Compensation Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of shares authorized for issuance under deferred compensation plan	222,220
Number of shares of common stock distributed	3,891	9,918