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

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, 2025	Dec. 31, 2024	Sep. 30, 2024
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	$ 1,678,314
Fiscal year before current fiscal year	1,207,232
Two years before current fiscal year	1,163,212
Three years before current fiscal year	1,174,721
Four years before current fiscal year	690,019
Prior	955,024
Revolving Loans Amortized Cost Basis	1,409,725
Total Loans	8,278,247	$ 8,025,110	$ 8,180,361
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	129,179
Fiscal year before current fiscal year	120,789
Two years before current fiscal year	132,867
Three years before current fiscal year	169,357
Four years before current fiscal year	134,782
Prior	230,293
Revolving Loans Amortized Cost Basis	20,709
Total Loans	937,976	931,709
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	75,122
Fiscal year before current fiscal year	70,456
Two years before current fiscal year	92,092
Three years before current fiscal year	117,486
Four years before current fiscal year	84,117
Prior	170,157
Revolving Loans Amortized Cost Basis	12,630
Total Loans	622,060
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	52,310
Fiscal year before current fiscal year	36,726
Two years before current fiscal year	29,313
Three years before current fiscal year	47,634
Four years before current fiscal year	45,787
Prior	55,469
Revolving Loans Amortized Cost Basis	7,883
Total Loans	275,122
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,747
Fiscal year before current fiscal year	4,024
Two years before current fiscal year	10,863
Three years before current fiscal year	4,224
Four years before current fiscal year	4,269
Prior	2,570
Revolving Loans Amortized Cost Basis	138
Total Loans	27,835
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	9,583
Two years before current fiscal year	599
Three years before current fiscal year	13
Four years before current fiscal year	609
Prior	2,097
Revolving Loans Amortized Cost Basis	58
Total Loans	12,959
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	284,734
Fiscal year before current fiscal year	202,248
Two years before current fiscal year	334,625
Three years before current fiscal year	404,170
Four years before current fiscal year	217,233
Prior	233,425
Revolving Loans Amortized Cost Basis	26,602
Total Loans	1,703,037	1,578,483
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	142,429
Fiscal year before current fiscal year	116,888
Two years before current fiscal year	176,137
Three years before current fiscal year	262,651
Four years before current fiscal year	114,698
Prior	154,866
Revolving Loans Amortized Cost Basis	11,887
Total Loans	979,556
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	138,949
Fiscal year before current fiscal year	66,898
Two years before current fiscal year	157,707
Three years before current fiscal year	140,525
Four years before current fiscal year	101,760
Prior	78,531
Revolving Loans Amortized Cost Basis	14,715
Total Loans	699,085
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	3,356
Two years before current fiscal year	666
Three years before current fiscal year	930
Four years before current fiscal year	513
Total Loans	5,465
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	17,840
Two years before current fiscal year	115
Three years before current fiscal year	64
Four years before current fiscal year	262
Prior	28
Total Loans	18,309
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	622
Total Loans	622
Real Estate [Member] \| Construction and Development Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	178,292
Fiscal year before current fiscal year	129,505
Two years before current fiscal year	153,728
Three years before current fiscal year	124,404
Four years before current fiscal year	8,599
Prior	27,703
Revolving Loans Amortized Cost Basis	39,651
Total Loans	661,882	756,662
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	90,161
Fiscal year before current fiscal year	84,331
Two years before current fiscal year	75,901
Three years before current fiscal year	86,717
Four years before current fiscal year	6,482
Prior	12,135
Revolving Loans Amortized Cost Basis	30,238
Total Loans	385,965
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	85,003
Fiscal year before current fiscal year	45,142
Two years before current fiscal year	77,790
Three years before current fiscal year	36,836
Four years before current fiscal year	1,901
Prior	15,312
Revolving Loans Amortized Cost Basis	9,413
Total Loans	271,397
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	3,069
Fiscal year before current fiscal year	32
Two years before current fiscal year	37
Three years before current fiscal year	35
Prior	117
Total Loans	3,290
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	59
Three years before current fiscal year	816
Four years before current fiscal year	216
Prior	139
Total Loans	1,230
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	185,574
Fiscal year before current fiscal year	47,640
Two years before current fiscal year	2,101
Three years before current fiscal year	2,647
Four years before current fiscal year	88
Prior	447
Revolving Loans Amortized Cost Basis	11,042
Total Loans	249,539	250,373
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	114,433
Fiscal year before current fiscal year	27,539
Two years before current fiscal year	1,948
Three years before current fiscal year	2,229
Four years before current fiscal year	88
Prior	447
Revolving Loans Amortized Cost Basis	5,385
Total Loans	152,069
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	68,991
Fiscal year before current fiscal year	19,229
Two years before current fiscal year	36
Three years before current fiscal year	212
Revolving Loans Amortized Cost Basis	5,549
Total Loans	94,017
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,337
Fiscal year before current fiscal year	250
Revolving Loans Amortized Cost Basis	108
Total Loans	1,695
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	813
Fiscal year before current fiscal year	622
Two years before current fiscal year	117
Three years before current fiscal year	206
Total Loans	1,758
Real Estate [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	261,310
Fiscal year before current fiscal year	282,603
Two years before current fiscal year	229,001
Three years before current fiscal year	227,288
Four years before current fiscal year	170,503
Prior	293,709
Revolving Loans Amortized Cost Basis	22,026
Total Loans	1,486,440	1,431,265
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	189,404
Fiscal year before current fiscal year	198,149
Two years before current fiscal year	171,404
Three years before current fiscal year	173,988
Four years before current fiscal year	128,007
Prior	220,927
Revolving Loans Amortized Cost Basis	5,147
Total Loans	1,087,026
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	65,536
Fiscal year before current fiscal year	77,693
Two years before current fiscal year	52,921
Three years before current fiscal year	49,467
Four years before current fiscal year	38,097
Prior	64,856
Revolving Loans Amortized Cost Basis	16,879
Total Loans	365,449
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	6,107
Fiscal year before current fiscal year	4,737
Two years before current fiscal year	3,461
Three years before current fiscal year	2,943
Four years before current fiscal year	3,254
Prior	5,711
Total Loans	26,213
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	263
Fiscal year before current fiscal year	2,024
Two years before current fiscal year	1,215
Three years before current fiscal year	890
Four years before current fiscal year	1,145
Prior	2,215
Total Loans	7,752
Real Estate [Member] \| Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	36,929
Fiscal year before current fiscal year	39,664
Two years before current fiscal year	25,918
Three years before current fiscal year	21,018
Four years before current fiscal year	6,043
Prior	18,487
Revolving Loans Amortized Cost Basis	157,235
Total Loans	305,294	275,461
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	30,361
Fiscal year before current fiscal year	32,299
Two years before current fiscal year	20,433
Three years before current fiscal year	16,989
Four years before current fiscal year	4,688
Prior	13,500
Revolving Loans Amortized Cost Basis	54,635
Total Loans	172,905
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	5,219
Fiscal year before current fiscal year	6,630
Two years before current fiscal year	4,810
Three years before current fiscal year	3,777
Four years before current fiscal year	1,079
Prior	4,373
Revolving Loans Amortized Cost Basis	98,709
Total Loans	124,597
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	877
Fiscal year before current fiscal year	667
Two years before current fiscal year	531
Three years before current fiscal year	184
Four years before current fiscal year	276
Prior	473
Revolving Loans Amortized Cost Basis	2,960
Total Loans	5,968
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	472
Fiscal year before current fiscal year	68
Two years before current fiscal year	144
Three years before current fiscal year	68
Prior	141
Revolving Loans Amortized Cost Basis	931
Total Loans	1,824
Real Estate [Member] \| Agriculture [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	82,085
Fiscal year before current fiscal year	56,647
Two years before current fiscal year	54,096
Three years before current fiscal year	49,747
Four years before current fiscal year	35,413
Prior	76,060
Revolving Loans Amortized Cost Basis	91,482
Total Loans	445,530	449,190
Real Estate [Member] \| Agriculture [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	38,300
Fiscal year before current fiscal year	27,196
Two years before current fiscal year	31,679
Three years before current fiscal year	30,379
Four years before current fiscal year	22,984
Prior	48,761
Revolving Loans Amortized Cost Basis	43,394
Total Loans	242,693
Real Estate [Member] \| Agriculture [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	42,272
Fiscal year before current fiscal year	27,054
Two years before current fiscal year	20,291
Three years before current fiscal year	15,840
Four years before current fiscal year	10,998
Prior	22,950
Revolving Loans Amortized Cost Basis	41,001
Total Loans	180,406
Real Estate [Member] \| Agriculture [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,403
Fiscal year before current fiscal year	1,654
Two years before current fiscal year	1,933
Three years before current fiscal year	2,782
Four years before current fiscal year	1,147
Prior	3,792
Revolving Loans Amortized Cost Basis	6,962
Total Loans	19,673
Real Estate [Member] \| Agriculture [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	110
Fiscal year before current fiscal year	743
Two years before current fiscal year	193
Three years before current fiscal year	746
Four years before current fiscal year	284
Prior	557
Revolving Loans Amortized Cost Basis	125
Total Loans	2,758
Commercial Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	192,325
Fiscal year before current fiscal year	175,301
Two years before current fiscal year	135,330
Three years before current fiscal year	130,783
Four years before current fiscal year	90,059
Prior	63,284
Revolving Loans Amortized Cost Basis	671,040
Total Loans	1,458,122	1,363,462
Commercial Non-real Estate [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	98,595
Fiscal year before current fiscal year	95,488
Two years before current fiscal year	62,924
Three years before current fiscal year	92,121
Four years before current fiscal year	80,450
Prior	55,739
Revolving Loans Amortized Cost Basis	389,275
Total Loans	874,592
Commercial Non-real Estate [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	91,386
Fiscal year before current fiscal year	77,032
Two years before current fiscal year	69,492
Three years before current fiscal year	36,190
Four years before current fiscal year	9,123
Prior	7,194
Revolving Loans Amortized Cost Basis	244,435
Total Loans	534,852
Commercial Non-real Estate [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,521
Fiscal year before current fiscal year	1,886
Two years before current fiscal year	1,916
Three years before current fiscal year	1,345
Four years before current fiscal year	359
Prior	125
Revolving Loans Amortized Cost Basis	37,068
Total Loans	44,220
Commercial Non-real Estate [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	823
Fiscal year before current fiscal year	577
Two years before current fiscal year	993
Three years before current fiscal year	910
Four years before current fiscal year	117
Prior	126
Revolving Loans Amortized Cost Basis	262
Total Loans	3,808
Commercial Non-real Estate [Member] \| Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	318
Two years before current fiscal year	5
Three years before current fiscal year	217
Four years before current fiscal year	10
Prior	100
Total Loans	650
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	185,124
Fiscal year before current fiscal year	134,015
Two years before current fiscal year	80,764
Three years before current fiscal year	38,512
Four years before current fiscal year	16,304
Prior	5,880
Revolving Loans Amortized Cost Basis	33,301
Total Loans	493,900	478,647
Consumer Non-real Estate [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	164,226
Fiscal year before current fiscal year	116,451
Two years before current fiscal year	66,756
Three years before current fiscal year	30,515
Four years before current fiscal year	12,935
Prior	4,518
Revolving Loans Amortized Cost Basis	16,981
Total Loans	412,382
Consumer Non-real Estate [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	17,942
Fiscal year before current fiscal year	15,570
Two years before current fiscal year	11,644
Three years before current fiscal year	6,669
Four years before current fiscal year	2,664
Prior	1,040
Revolving Loans Amortized Cost Basis	16,307
Total Loans	71,836
Consumer Non-real Estate [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,081
Fiscal year before current fiscal year	1,463
Two years before current fiscal year	1,663
Three years before current fiscal year	834
Four years before current fiscal year	530
Prior	257
Revolving Loans Amortized Cost Basis	10
Total Loans	5,838
Consumer Non-real Estate [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,875
Fiscal year before current fiscal year	531
Two years before current fiscal year	701
Three years before current fiscal year	494
Four years before current fiscal year	175
Prior	65
Revolving Loans Amortized Cost Basis	3
Total Loans	3,844
Oil and Gas [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	142,762
Fiscal year before current fiscal year	18,820
Two years before current fiscal year	14,782
Three years before current fiscal year	6,795
Four years before current fiscal year	10,995
Prior	5,736
Revolving Loans Amortized Cost Basis	336,637
Total Loans	536,527	$ 509,858
Oil and Gas [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	89,940
Fiscal year before current fiscal year	10,827
Two years before current fiscal year	9,121
Three years before current fiscal year	3,508
Four years before current fiscal year	8,234
Prior	2,643
Revolving Loans Amortized Cost Basis	258,117
Total Loans	382,390
Oil and Gas [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	51,855
Fiscal year before current fiscal year	7,976
Two years before current fiscal year	5,628
Three years before current fiscal year	3,287
Four years before current fiscal year	2,571
Prior	2,709
Revolving Loans Amortized Cost Basis	76,250
Total Loans	150,276
Oil and Gas [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	967
Fiscal year before current fiscal year	17
Two years before current fiscal year	33
Four years before current fiscal year	154
Prior	40
Revolving Loans Amortized Cost Basis	2,270
Total Loans	3,481
Oil and Gas [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Four years before current fiscal year	36
Prior	344
Total Loans	$ 380