Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Segment Reporting Information [Line Items]
Net interest income	$ 106,104	$ 109,156
Noninterest income	44,900	47,828
Income before taxes	64,210	74,345
Total assets	12,602,425		$ 12,372,042
Operating Segments [Member] | BancFirst Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Net interest income	28,193	30,739
Noninterest income	5,169	6,087
Income before taxes	22,331	23,310
Total assets	3,283,434		3,598,888
Operating Segments [Member] | BancFirst Community Banks [Member]
Segment Reporting Information [Line Items]
Net interest income	60,011	57,685
Noninterest income	15,918	19,532
Income before taxes	38,792	43,599
Total assets	7,452,457		7,012,905
Operating Segments [Member] | Pegasus [Member]
Segment Reporting Information [Line Items]
Net interest income	10,867	15,151
Noninterest income	320	214
Income before taxes	3,145	9,644
Total assets	1,322,543		1,280,618
Operating Segments [Member] | Worthington [Member]
Segment Reporting Information [Line Items]
Net interest income	4,389	4,624
Noninterest income	221	279
Income before taxes	669	1,630
Total assets	618,111		600,364
Operating Segments [Member] | Other Financial Services [Member]
Segment Reporting Information [Line Items]
Net interest income	1,019	942
Noninterest income	15,163	14,172
Income before taxes	6,335	6,164
Total assets	111,953		121,601
Operating Segments [Member] | Executive, Operations & Support [Member]
Segment Reporting Information [Line Items]
Net interest income	1,625	15
Noninterest income	58,428	66,143
Income before taxes	43,071	48,417
Total assets	1,404,833		1,307,714
Eliminations [Member]
Segment Reporting Information [Line Items]
Noninterest income	(50,319)	(58,599)
Income before taxes	(50,133)	$ (58,419)
Total assets	$ (1,590,906)		$ (1,550,048)