Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Net interest income	$ 104,308	$ 100,947	$ 319,390	$ 263,321
Noninterest income	44,449	49,331	140,251	135,579
Income before taxes	65,230	68,337	209,541	167,293
Total assets	12,114,602		12,114,602		$ 12,387,863
Operating Segments [Member] | BancFirst Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income	30,258	26,022	90,266	67,592
Noninterest income	5,533	8,722	18,710	23,999
Income before taxes	22,043	22,827	66,941	56,140
Total assets	3,533,334		3,533,334		3,412,369
Operating Segments [Member] | BancFirst Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income	56,644	55,782	171,946	149,965
Noninterest income	15,986	18,764	55,504	53,761
Income before taxes	38,985	41,179	125,768	108,980
Total assets	6,929,256		6,929,256		6,886,066
Operating Segments [Member] | Pegasus [Member]
Segment Reporting Information [Line Items]
Net interest income	11,334	13,815	39,994	31,399
Noninterest income	561	246	1,242	730
Income before taxes	6,559	8,178	26,060	15,677
Total assets	1,308,938		1,308,938		1,404,033
Operating Segments [Member] | Worthington [Member]
Segment Reporting Information [Line Items]
Net interest income	4,160	4,723	12,907	10,160
Noninterest income	301	305	835	724
Income before taxes	693	2,109	3,114	3,930
Total assets	574,929		574,929		541,002
Operating Segments [Member] | Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income	1,063	1,604	3,063	6,596
Noninterest income	14,542	14,106	41,064	37,842
Income before taxes	5,541	6,222	16,003	16,910
Total assets	62,118		62,118		171,679
Operating Segments [Member] | Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income	849	(999)	1,214	(2,411)
Noninterest income	59,923	62,969	189,754	158,299
Income before taxes	43,282	43,180	137,624	104,729
Total assets	1,212,338		1,212,338		1,473,443
Eliminations [Member]
Segment Reporting Information [Line Items]
Net interest income				20
Noninterest income	(52,397)	(55,781)	(166,858)	(139,776)
Income before taxes	(51,873)	$ (55,358)	(165,969)	$ (139,073)
Total assets	$ (1,506,311)		$ (1,506,311)		$ (1,500,729)