Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Segment Reporting Information [Line Items]
Net interest income	$ 109,896	$ 105,926	$ 216,000	$ 215,082
Noninterest income	43,944	47,974	88,844	95,802
Income before taxes	65,166	69,966	129,376	144,311
Total assets	12,737,318		12,737,318		$ 12,372,042
Operating Segments [Member] | BancFirst Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income	29,139	29,269	57,332	60,008
Noninterest income	5,562	7,090	10,731	13,177
Income before taxes	21,209	21,588	43,540	44,898
Total assets	3,365,250		3,365,250		3,598,888
Operating Segments [Member] | BancFirst Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income	61,710	57,617	121,721	115,302
Noninterest income	16,886	19,986	32,804	39,518
Income before taxes	42,267	43,184	81,059	86,783
Total assets	7,489,606		7,489,606		7,012,905
Operating Segments [Member] | Pegasus [Member]
Segment Reporting Information [Line Items]
Net interest income	11,363	13,509	22,230	28,660
Noninterest income	339	467	659	681
Income before taxes	6,112	9,857	9,257	19,501
Total assets	1,360,612		1,360,612		1,280,618
Operating Segments [Member] | Worthington [Member]
Segment Reporting Information [Line Items]
Net interest income	4,462	4,123	8,851	8,747
Noninterest income	250	255	471	534
Income before taxes	744	791	1,413	2,421
Total assets	622,902		622,902		600,364
Operating Segments [Member] | Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income	1,103	1,058	2,122	2,000
Noninterest income	13,513	12,350	28,676	26,522
Income before taxes	4,139	4,298	10,474	10,462
Total assets	121,308		121,308		121,601
Operating Segments [Member] | Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income	2,119	350	3,744	365
Noninterest income	58,064	63,688	116,492	129,831
Income before taxes	41,225	45,925	84,296	94,342
Total assets	1,392,169		1,392,169		1,307,714
Eliminations [Member]
Segment Reporting Information [Line Items]
Noninterest income	(50,670)	(55,862)	(100,989)	(114,461)
Income before taxes	(50,530)	$ (55,677)	(100,663)	$ (114,096)
Total assets	$ (1,614,529)		$ (1,614,529)		$ (1,550,048)