Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Segment Reporting Information [Line Items]
Net interest income	$ 109,156	$ 75,507
Noninterest income	47,828	43,650
Income before taxes	74,345	43,709
Total assets	12,332,105		$ 12,387,863
Operating Segments [Member] | BancFirst Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income	30,739	19,608
Noninterest income	6,087	9,773
Income before taxes	23,310	18,171
Total assets	3,413,494		3,412,369
Operating Segments [Member] | BancFirst Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income	57,685	44,568
Noninterest income	19,532	16,845
Income before taxes	43,599	31,339
Total assets	6,817,850		6,886,066
Operating Segments [Member] | Pegasus [Member]
Segment Reporting Information [Line Items]
Net interest income	15,151	7,620
Noninterest income	214	191
Income before taxes	9,644	2,827
Total assets	1,390,459		1,404,033
Operating Segments [Member] | Worthington [Member]
Segment Reporting Information [Line Items]
Net interest income	4,624	1,694
Noninterest income	279	133
Income before taxes	1,630	385
Total assets	516,112		541,002
Operating Segments [Member] | Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income	942	2,913
Noninterest income	14,172	12,983
Income before taxes	6,164	6,045
Total assets	147,971		171,679
Operating Segments [Member] | Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income	15	(907)
Noninterest income	66,143	42,574
Income before taxes	48,417	23,648
Total assets	1,491,908		1,473,443
Eliminations [Member]
Segment Reporting Information [Line Items]
Net interest income		11
Noninterest income	(58,599)	(38,849)
Income before taxes	(58,419)	$ (38,706)
Total assets	$ (1,445,689)		$ (1,500,729)