Segment Information - Results of Operations and Selected Financial Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Segment Reporting Information [Line Items]
Interest income	$ 188,427	$ 178,465	$ 370,903	$ 350,108
Interest expense	67,171	68,569	133,698	134,108
Total provision for/(benefit from) credit losses	1,387	3,358	2,973	7,373
Noninterest income	48,048	43,944	96,942	88,844
Depreciation and amortization	5,553	5,391	11,247	10,833
Other noninterest expense	82,646	79,925	169,131	157,262
Income before taxes	79,718	65,166	150,796	129,376
Capital expenditures			25,054	16,273
Loans held for investment	8,114,488	8,047,448	8,114,488	8,047,448	$ 8,025,110
Total assets	14,045,780	12,737,318	14,045,780	12,737,318	13,554,314
Deposits	12,056,192	11,015,602	12,056,192	11,015,602	$ 11,718,546
Operating Segments [Member] | BancFirst Metropolitan Banks [Member]
Segment Reporting Information [Line Items]
Interest income	49,285	52,828	98,671	103,804
Interest expense	19,938	23,689	40,467	46,472
Total provision for/(benefit from) credit losses	484	1,949	433	1,705
Noninterest income	6,296	5,562	12,523	10,731
Depreciation and amortization	386	536	866	1,083
Other noninterest expense	11,939	11,007	23,501	21,735
Income before taxes	22,834	21,209	45,927	43,540
Capital expenditures			2,511	2,501
Loans held for investment	2,466,154	2,564,689	2,466,154	2,564,689
Total assets	3,443,579	3,365,250	3,443,579	3,365,250
Deposits	2,961,647	2,560,657	2,961,647	2,560,657
Operating Segments [Member] | BancFirst Community Banks [Member]
Segment Reporting Information [Line Items]
Interest income	109,469	102,615	215,081	201,493
Interest expense	40,099	40,905	79,564	79,772
Total provision for/(benefit from) credit losses	270	1,169	1,457	2,492
Noninterest income	18,681	16,886	36,427	32,804
Depreciation and amortization	2,627	2,457	5,280	4,921
Other noninterest expense	35,812	32,703	70,538	66,053
Income before taxes	49,342	42,267	94,669	81,059
Capital expenditures			6,815	5,024
Loans held for investment	4,114,132	4,021,062	4,114,132	4,021,062
Total assets	8,091,096	7,489,606	8,091,096	7,489,606
Deposits	7,454,342	6,874,717	7,454,342	6,874,717
Operating Segments [Member] | Pegasus [Member]
Segment Reporting Information [Line Items]
Interest income	20,394	19,533	40,103	38,397
Interest expense	7,701	8,170	14,886	16,167
Total provision for/(benefit from) credit losses	111	130	216	2,860
Noninterest income	617	339	1,176	659
Depreciation and amortization	147	151	295	332
Other noninterest expense	5,583	5,309	11,225	10,440
Income before taxes	7,469	6,112	14,657	9,257
Capital expenditures			387	43
Loans held for investment	887,498	829,826	887,498	829,826
Total assets	1,487,269	1,360,612	1,487,269	1,360,612
Deposits	1,265,357	1,158,662	1,265,357	1,158,662
Operating Segments [Member] | Worthington [Member]
Segment Reporting Information [Line Items]
Interest income	9,063	7,832	17,656	15,342
Interest expense	2,994	3,370	6,191	6,491
Total provision for/(benefit from) credit losses	211	67	343	189
Noninterest income	236	250	465	471
Depreciation and amortization	161	159	329	320
Other noninterest expense	3,751	3,742	7,513	7,400
Income before taxes	2,182	744	3,745	1,413
Capital expenditures			87	4,658
Loans held for investment	479,897	446,972	479,897	446,972
Total assets	619,458	622,902	619,458	622,902
Deposits	530,347	522,487	530,347	522,487
Operating Segments [Member] | Other Financial Services [Member]
Segment Reporting Information [Line Items]
Interest income	2,638	2,368	5,014	4,672
Interest expense	979	1,265	1,958	2,550
Total provision for/(benefit from) credit losses	(7)	25	11	68
Noninterest income	14,171	13,513	30,833	28,676
Depreciation and amortization	126	125	269	245
Other noninterest expense	9,344	10,327	23,961	20,011
Income before taxes	6,367	4,139	9,648	10,474
Capital expenditures			887	13
Loans held for investment	95,326	97,044	95,326	97,044
Total assets	174,366	121,308	174,366	121,308
Intersegment elimation [Member] | Executive, Operations, Support and Eliminations [Member]
Segment Reporting Information [Line Items]
Interest income	(2,422)	(6,711)	(5,622)	(13,600)
Interest expense	(4,540)	(8,830)	(9,368)	(17,344)
Total provision for/(benefit from) credit losses	318	18	513	59
Noninterest income	8,047	7,394	15,518	15,503
Depreciation and amortization	2,106	1,963	4,208	3,932
Other noninterest expense	16,217	16,837	32,393	31,623
Income before taxes	(8,476)	(9,305)	(17,850)	(16,367)
Capital expenditures			14,367	4,034
Loans held for investment	71,481	87,855	71,481	87,855
Total assets	230,012	(222,360)	230,012	(222,360)
Deposits	$ (155,501)	$ (100,921)	$ (155,501)	$ (100,921)