Loans Held for Investment and Allowance for Credit Losses on Loans - Gross Loans Held for Investment by Year of Origination and Internally Assigned Credit Grades (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	$ 1,778,095
Fiscal year before current fiscal year	1,666,144
Two years before current fiscal year	1,140,507
Three years before current fiscal year	598,579
Four years before current fiscal year	443,476
Prior	675,202
Revolving Loans Amortized Cost Basis	1,170,619
Total loans	7,472,622	$ 6,943,563
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	129,971
Fiscal year before current fiscal year	217,176
Two years before current fiscal year	162,237
Three years before current fiscal year	112,921
Four years before current fiscal year	106,493
Prior	171,500
Revolving Loans Amortized Cost Basis	60,570
Total loans	960,868	908,494
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	99,990
Fiscal year before current fiscal year	155,460
Two years before current fiscal year	120,444
Three years before current fiscal year	87,838
Four years before current fiscal year	82,081
Prior	139,298
Revolving Loans Amortized Cost Basis	23,622
Total loans	708,733
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	29,812
Fiscal year before current fiscal year	57,975
Two years before current fiscal year	37,289
Three years before current fiscal year	23,581
Four years before current fiscal year	21,509
Prior	30,107
Revolving Loans Amortized Cost Basis	34,361
Total loans	234,634
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	142
Fiscal year before current fiscal year	3,582
Two years before current fiscal year	4,304
Three years before current fiscal year	652
Four years before current fiscal year	1,899
Prior	1,075
Revolving Loans Amortized Cost Basis	2,437
Total loans	14,091
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	27
Fiscal year before current fiscal year	159
Two years before current fiscal year	200
Three years before current fiscal year	850
Four years before current fiscal year	665
Prior	1,020
Revolving Loans Amortized Cost Basis	150
Total loans	3,071
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
Four years before current fiscal year	339
Total loans	339
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	235,363
Fiscal year before current fiscal year	418,523
Two years before current fiscal year	260,164
Three years before current fiscal year	176,538
Four years before current fiscal year	129,169
Prior	147,572
Revolving Loans Amortized Cost Basis	76,502
Total loans	1,443,831	1,383,150
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	160,303
Fiscal year before current fiscal year	255,862
Two years before current fiscal year	176,995
Three years before current fiscal year	122,636
Four years before current fiscal year	59,973
Prior	72,918
Revolving Loans Amortized Cost Basis	47,780
Total loans	896,467
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	74,860
Fiscal year before current fiscal year	155,293
Two years before current fiscal year	81,452
Three years before current fiscal year	53,753
Four years before current fiscal year	62,989
Prior	73,789
Revolving Loans Amortized Cost Basis	28,722
Total loans	530,858
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	6,736
Two years before current fiscal year	1,717
Three years before current fiscal year	149
Four years before current fiscal year	6,207
Prior	299
Total loans	15,108
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	200
Fiscal year before current fiscal year	632
Prior	566
Total loans	1,398
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	154,693
Fiscal year before current fiscal year	175,378
Two years before current fiscal year	106,340
Three years before current fiscal year	15,210
Four years before current fiscal year	20,414
Prior	7,793
Revolving Loans Amortized Cost Basis	95,824
Total loans	575,652	475,236
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	91,548
Fiscal year before current fiscal year	123,068
Two years before current fiscal year	73,070
Three years before current fiscal year	8,484
Four years before current fiscal year	6,842
Prior	5,403
Revolving Loans Amortized Cost Basis	61,474
Total loans	369,889
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	59,837
Fiscal year before current fiscal year	50,514
Two years before current fiscal year	33,168
Three years before current fiscal year	6,629
Four years before current fiscal year	13,572
Prior	2,381
Revolving Loans Amortized Cost Basis	34,350
Total loans	200,451
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	3,308
Fiscal year before current fiscal year	893
Two years before current fiscal year	102
Three years before current fiscal year	97
Prior	7
Total loans	4,407
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	903
Prior	2
Total loans	905
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	187,674
Fiscal year before current fiscal year	46,891
Two years before current fiscal year	1,473
Three years before current fiscal year	124
Four years before current fiscal year	2
Prior	419
Revolving Loans Amortized Cost Basis	37,728
Total loans	274,311	303,305
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	136,871
Fiscal year before current fiscal year	36,431
Two years before current fiscal year	1,441
Three years before current fiscal year	102
Four years before current fiscal year	2
Prior	37
Revolving Loans Amortized Cost Basis	37,179
Total loans	212,063
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	44,707
Fiscal year before current fiscal year	9,530
Two years before current fiscal year	32
Three years before current fiscal year	22
Prior	382
Revolving Loans Amortized Cost Basis	549
Total loans	55,222
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	5,730
Fiscal year before current fiscal year	387
Total loans	6,117
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	366
Fiscal year before current fiscal year	543
Total loans	909
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	267,873
Fiscal year before current fiscal year	281,659
Two years before current fiscal year	220,274
Three years before current fiscal year	148,438
Four years before current fiscal year	89,679
Prior	205,667
Revolving Loans Amortized Cost Basis	2,918
Total loans	1,216,508	1,117,899
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	223,552
Fiscal year before current fiscal year	238,614
Two years before current fiscal year	177,122
Three years before current fiscal year	121,747
Four years before current fiscal year	74,016
Prior	155,802
Revolving Loans Amortized Cost Basis	2,918
Total loans	993,771
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	41,655
Fiscal year before current fiscal year	40,971
Two years before current fiscal year	39,280
Three years before current fiscal year	25,018
Four years before current fiscal year	13,617
Prior	43,460
Total loans	204,001
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	2,282
Fiscal year before current fiscal year	1,902
Two years before current fiscal year	2,626
Three years before current fiscal year	1,327
Four years before current fiscal year	1,606
Prior	4,202
Total loans	13,945
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	384
Fiscal year before current fiscal year	172
Two years before current fiscal year	1,246
Three years before current fiscal year	346
Four years before current fiscal year	440
Prior	2,203
Total loans	4,791
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	38,666
Fiscal year before current fiscal year	32,804
Two years before current fiscal year	10,450
Three years before current fiscal year	10,242
Four years before current fiscal year	5,645
Prior	16,802
Revolving Loans Amortized Cost Basis	115,788
Total loans	230,397	196,198
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	35,422
Fiscal year before current fiscal year	27,339
Two years before current fiscal year	8,166
Three years before current fiscal year	8,242
Four years before current fiscal year	3,963
Prior	13,045
Revolving Loans Amortized Cost Basis	41,474
Total loans	137,651
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	2,828
Fiscal year before current fiscal year	5,088
Two years before current fiscal year	2,210
Three years before current fiscal year	1,958
Four years before current fiscal year	1,546
Prior	3,272
Revolving Loans Amortized Cost Basis	71,527
Total loans	88,429
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	416
Fiscal year before current fiscal year	353
Two years before current fiscal year	74
Three years before current fiscal year	42
Four years before current fiscal year	41
Prior	440
Revolving Loans Amortized Cost Basis	1,925
Total loans	3,291
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	24
Four years before current fiscal year	95
Prior	45
Revolving Loans Amortized Cost Basis	862
Total loans	1,026
Real Estate [Member] | Agriculture [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	84,850
Fiscal year before current fiscal year	81,414
Two years before current fiscal year	56,745
Three years before current fiscal year	43,154
Four years before current fiscal year	27,939
Prior	53,896
Revolving Loans Amortized Cost Basis	77,932
Total loans	425,930	408,037
Real Estate [Member] | Agriculture [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	47,552
Fiscal year before current fiscal year	55,420
Two years before current fiscal year	35,685
Three years before current fiscal year	29,284
Four years before current fiscal year	17,863
Prior	33,652
Revolving Loans Amortized Cost Basis	39,462
Total loans	258,918
Real Estate [Member] | Agriculture [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	28,366
Fiscal year before current fiscal year	24,237
Two years before current fiscal year	19,989
Three years before current fiscal year	10,303
Four years before current fiscal year	9,369
Prior	17,304
Revolving Loans Amortized Cost Basis	35,554
Total loans	145,122
Real Estate [Member] | Agriculture [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	8,891
Fiscal year before current fiscal year	856
Two years before current fiscal year	854
Three years before current fiscal year	3,433
Four years before current fiscal year	323
Prior	2,696
Revolving Loans Amortized Cost Basis	2,896
Total loans	19,949
Real Estate [Member] | Agriculture [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	41
Fiscal year before current fiscal year	901
Two years before current fiscal year	217
Three years before current fiscal year	134
Four years before current fiscal year	384
Prior	244
Revolving Loans Amortized Cost Basis	20
Total loans	1,941
Commercial Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	288,089
Fiscal year before current fiscal year	234,558
Two years before current fiscal year	194,909
Three years before current fiscal year	56,425
Four years before current fiscal year	50,203
Prior	49,729
Revolving Loans Amortized Cost Basis	422,883
Total loans	1,296,796	1,241,454
Commercial Non-real Estate [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	204,828
Fiscal year before current fiscal year	186,934
Two years before current fiscal year	167,915
Three years before current fiscal year	40,328
Four years before current fiscal year	39,003
Prior	39,326
Revolving Loans Amortized Cost Basis	281,116
Total loans	959,450
Commercial Non-real Estate [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	80,383
Fiscal year before current fiscal year	43,067
Two years before current fiscal year	25,617
Three years before current fiscal year	15,244
Four years before current fiscal year	10,064
Prior	9,171
Revolving Loans Amortized Cost Basis	137,965
Total loans	321,511
Commercial Non-real Estate [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,840
Fiscal year before current fiscal year	3,149
Two years before current fiscal year	1,073
Three years before current fiscal year	163
Four years before current fiscal year	563
Prior	1,103
Revolving Loans Amortized Cost Basis	2,648
Total loans	10,539
Commercial Non-real Estate [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,038
Fiscal year before current fiscal year	1,408
Two years before current fiscal year	304
Three years before current fiscal year	690
Four years before current fiscal year	309
Prior	129
Revolving Loans Amortized Cost Basis	1,154
Total loans	5,032
Commercial Non-real Estate [Member] | Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
Four years before current fiscal year	264
Total loans	264
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	191,515
Fiscal year before current fiscal year	141,784
Two years before current fiscal year	73,413
Three years before current fiscal year	25,261
Four years before current fiscal year	11,983
Prior	5,299
Revolving Loans Amortized Cost Basis	26,466
Total loans	475,721	446,756
Consumer Non-real Estate [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	175,483
Fiscal year before current fiscal year	123,675
Two years before current fiscal year	64,280
Three years before current fiscal year	22,331
Four years before current fiscal year	10,804
Prior	3,518
Revolving Loans Amortized Cost Basis	24,688
Total loans	424,779
Consumer Non-real Estate [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	15,347
Fiscal year before current fiscal year	16,509
Two years before current fiscal year	7,792
Three years before current fiscal year	2,502
Four years before current fiscal year	809
Prior	1,614
Revolving Loans Amortized Cost Basis	1,764
Total loans	46,337
Consumer Non-real Estate [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	562
Fiscal year before current fiscal year	1,198
Two years before current fiscal year	957
Three years before current fiscal year	325
Four years before current fiscal year	285
Prior	155
Revolving Loans Amortized Cost Basis	12
Total loans	3,494
Consumer Non-real Estate [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	123
Fiscal year before current fiscal year	402
Two years before current fiscal year	384
Three years before current fiscal year	103
Four years before current fiscal year	85
Prior	12
Revolving Loans Amortized Cost Basis	2
Total loans	1,111
Oil and Gas [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	199,401
Fiscal year before current fiscal year	35,957
Two years before current fiscal year	54,502
Three years before current fiscal year	10,266
Four years before current fiscal year	1,949
Prior	16,525
Revolving Loans Amortized Cost Basis	254,008
Total loans	572,608	$ 463,034
Oil and Gas [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	157,820
Fiscal year before current fiscal year	26,772
Two years before current fiscal year	52,090
Three years before current fiscal year	9,850
Four years before current fiscal year	1,630
Prior	16,141
Revolving Loans Amortized Cost Basis	170,256
Total loans	434,559
Oil and Gas [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	41,447
Fiscal year before current fiscal year	7,180
Two years before current fiscal year	1,999
Three years before current fiscal year	414
Four years before current fiscal year	306
Prior	217
Revolving Loans Amortized Cost Basis	83,009
Total loans	134,572
Oil and Gas [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	134
Fiscal year before current fiscal year	1,922
Two years before current fiscal year	413
Three years before current fiscal year	2
Four years before current fiscal year	13
Prior	167
Revolving Loans Amortized Cost Basis	743
Total loans	3,394
Oil and Gas [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	83
Total loans	$ 83