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	Jun. 30, 2025	Dec. 31, 2024	Jun. 30, 2024
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	$ 1,167,242
Fiscal year before current fiscal year	1,365,067
Two years before current fiscal year	1,256,904
Three years before current fiscal year	1,255,679
Four years before current fiscal year	730,539
Prior	1,021,604
Revolving Loans Amortized Cost Basis	1,317,453
Total Loans	8,114,488	$ 8,025,110	$ 8,047,448
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	85,163
Fiscal year before current fiscal year	122,155
Two years before current fiscal year	147,141
Three years before current fiscal year	177,728
Four years before current fiscal year	139,100
Prior	246,072
Revolving Loans Amortized Cost Basis	20,067
Total Loans	937,426	931,709
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	46,987
Fiscal year before current fiscal year	72,680
Two years before current fiscal year	103,525
Three years before current fiscal year	126,529
Four years before current fiscal year	89,591
Prior	184,795
Revolving Loans Amortized Cost Basis	12,575
Total Loans	636,682
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	37,790
Fiscal year before current fiscal year	35,379
Two years before current fiscal year	32,027
Three years before current fiscal year	47,992
Four years before current fiscal year	46,707
Prior	57,105
Revolving Loans Amortized Cost Basis	7,354
Total Loans	264,354
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	386
Fiscal year before current fiscal year	13,853
Two years before current fiscal year	10,990
Three years before current fiscal year	3,054
Four years before current fiscal year	2,244
Prior	1,865
Revolving Loans Amortized Cost Basis	138
Total Loans	32,530
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	243
Two years before current fiscal year	599
Three years before current fiscal year	153
Four years before current fiscal year	558
Prior	2,307
Total Loans	3,860
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	152,385
Fiscal year before current fiscal year	217,461
Two years before current fiscal year	370,764
Three years before current fiscal year	418,504
Four years before current fiscal year	220,824
Prior	251,224
Revolving Loans Amortized Cost Basis	43,067
Total Loans	1,674,229	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	94,690
Fiscal year before current fiscal year	115,357
Two years before current fiscal year	256,328
Three years before current fiscal year	284,008
Four years before current fiscal year	155,649
Prior	168,459
Revolving Loans Amortized Cost Basis	29,140
Total Loans	1,103,631
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	53,516
Fiscal year before current fiscal year	82,637
Two years before current fiscal year	114,315
Three years before current fiscal year	133,489
Four years before current fiscal year	64,902
Prior	82,708
Revolving Loans Amortized Cost Basis	13,927
Total Loans	545,494
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	4,179
Three years before current fiscal year	943
Total Loans	5,122
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	19,467
Two years before current fiscal year	121
Three years before current fiscal year	64
Four years before current fiscal year	273
Prior	57
Total Loans	19,982
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	169,073
Fiscal year before current fiscal year	161,012
Two years before current fiscal year	135,710
Three years before current fiscal year	140,284
Four years before current fiscal year	9,110
Prior	28,743
Revolving Loans Amortized Cost Basis	40,359
Total Loans	684,291	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	68,650
Fiscal year before current fiscal year	102,545
Two years before current fiscal year	101,111
Three years before current fiscal year	108,571
Four years before current fiscal year	7,853
Prior	13,230
Revolving Loans Amortized Cost Basis	31,451
Total Loans	433,411
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	97,774
Fiscal year before current fiscal year	57,984
Two years before current fiscal year	34,458
Three years before current fiscal year	30,861
Four years before current fiscal year	608
Prior	15,252
Revolving Loans Amortized Cost Basis	8,908
Total Loans	245,845
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	2,588
Fiscal year before current fiscal year	483
Two years before current fiscal year	123
Three years before current fiscal year	36
Four years before current fiscal year	346
Prior	125
Total Loans	3,701
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	61
Two years before current fiscal year	18
Three years before current fiscal year	816
Four years before current fiscal year	303
Prior	136
Total Loans	1,334
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	122,751
Fiscal year before current fiscal year	85,116
Two years before current fiscal year	8,631
Three years before current fiscal year	5,738
Four years before current fiscal year	88
Prior	1,749
Revolving Loans Amortized Cost Basis	10,959
Total Loans	235,032	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	69,559
Fiscal year before current fiscal year	50,902
Two years before current fiscal year	7,351
Three years before current fiscal year	4,780
Four years before current fiscal year	88
Prior	1,749
Revolving Loans Amortized Cost Basis	3,847
Total Loans	138,276
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	51,610
Fiscal year before current fiscal year	33,149
Two years before current fiscal year	1,163
Three years before current fiscal year	752
Revolving Loans Amortized Cost Basis	7,112
Total Loans	93,786
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	769
Fiscal year before current fiscal year	320
Total Loans	1,089
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	745
Two years before current fiscal year	117
Three years before current fiscal year	206
Total Loans	1,881
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	168,632
Fiscal year before current fiscal year	302,094
Two years before current fiscal year	242,960
Three years before current fiscal year	238,267
Four years before current fiscal year	178,522
Prior	310,355
Revolving Loans Amortized Cost Basis	21,928
Total Loans	1,462,758	1,431,265
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	126,178
Fiscal year before current fiscal year	216,760
Two years before current fiscal year	182,841
Three years before current fiscal year	183,960
Four years before current fiscal year	134,645
Prior	237,448
Revolving Loans Amortized Cost Basis	4,914
Total Loans	1,086,746
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	38,500
Fiscal year before current fiscal year	76,142
Two years before current fiscal year	55,034
Three years before current fiscal year	50,662
Four years before current fiscal year	39,334
Prior	64,838
Revolving Loans Amortized Cost Basis	17,014
Total Loans	341,524
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	3,873
Fiscal year before current fiscal year	5,302
Two years before current fiscal year	3,922
Three years before current fiscal year	2,792
Four years before current fiscal year	2,726
Prior	5,738
Total Loans	24,353
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	81
Fiscal year before current fiscal year	3,890
Two years before current fiscal year	1,163
Three years before current fiscal year	853
Four years before current fiscal year	1,817
Prior	2,331
Total Loans	10,135
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	22,769
Fiscal year before current fiscal year	39,816
Two years before current fiscal year	28,517
Three years before current fiscal year	21,123
Four years before current fiscal year	6,240
Prior	19,641
Revolving Loans Amortized Cost Basis	153,256
Total Loans	291,362	275,461
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	18,436
Fiscal year before current fiscal year	32,547
Two years before current fiscal year	22,572
Three years before current fiscal year	17,121
Four years before current fiscal year	4,829
Prior	14,150
Revolving Loans Amortized Cost Basis	53,812
Total Loans	163,467
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	3,461
Fiscal year before current fiscal year	6,586
Two years before current fiscal year	5,321
Three years before current fiscal year	3,761
Four years before current fiscal year	1,174
Prior	4,928
Revolving Loans Amortized Cost Basis	95,954
Total Loans	121,185
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	453
Fiscal year before current fiscal year	615
Two years before current fiscal year	480
Three years before current fiscal year	124
Four years before current fiscal year	221
Prior	383
Revolving Loans Amortized Cost Basis	2,025
Total Loans	4,301
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	419
Fiscal year before current fiscal year	68
Two years before current fiscal year	144
Three years before current fiscal year	117
Four years before current fiscal year	16
Prior	180
Revolving Loans Amortized Cost Basis	1,465
Total Loans	2,409
Real Estate [Member] | Agriculture [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	55,836
Fiscal year before current fiscal year	65,575
Two years before current fiscal year	58,969
Three years before current fiscal year	53,535
Four years before current fiscal year	38,332
Prior	80,442
Revolving Loans Amortized Cost Basis	95,295
Total Loans	447,984	449,190
Real Estate [Member] | Agriculture [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	26,222
Fiscal year before current fiscal year	31,946
Two years before current fiscal year	34,820
Three years before current fiscal year	33,569
Four years before current fiscal year	24,882
Prior	52,665
Revolving Loans Amortized Cost Basis	51,487
Total Loans	255,591
Real Estate [Member] | Agriculture [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	28,619
Fiscal year before current fiscal year	31,678
Two years before current fiscal year	21,831
Three years before current fiscal year	16,658
Four years before current fiscal year	11,838
Prior	23,148
Revolving Loans Amortized Cost Basis	37,213
Total Loans	170,985
Real Estate [Member] | Agriculture [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	964
Fiscal year before current fiscal year	1,158
Two years before current fiscal year	1,905
Three years before current fiscal year	2,550
Four years before current fiscal year	1,287
Prior	4,260
Revolving Loans Amortized Cost Basis	6,470
Total Loans	18,594
Real Estate [Member] | Agriculture [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	31
Fiscal year before current fiscal year	793
Two years before current fiscal year	413
Three years before current fiscal year	758
Four years before current fiscal year	325
Prior	369
Revolving Loans Amortized Cost Basis	125
Total Loans	2,814
Commercial Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	161,108
Fiscal year before current fiscal year	191,144
Two years before current fiscal year	152,020
Three years before current fiscal year	146,494
Four years before current fiscal year	97,777
Prior	69,242
Revolving Loans Amortized Cost Basis	609,791
Total Loans	1,427,576	1,363,462
Commercial Non-real Estate [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	91,468
Fiscal year before current fiscal year	119,790
Two years before current fiscal year	83,645
Three years before current fiscal year	118,094
Four years before current fiscal year	87,175
Prior	61,279
Revolving Loans Amortized Cost Basis	350,751
Total Loans	912,202
Commercial Non-real Estate [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	68,090
Fiscal year before current fiscal year	69,535
Two years before current fiscal year	65,733
Three years before current fiscal year	26,150
Four years before current fiscal year	10,115
Prior	7,364
Revolving Loans Amortized Cost Basis	222,337
Total Loans	469,324
Commercial Non-real Estate [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	774
Fiscal year before current fiscal year	1,283
Two years before current fiscal year	1,600
Three years before current fiscal year	1,024
Four years before current fiscal year	328
Prior	171
Revolving Loans Amortized Cost Basis	36,378
Total Loans	41,558
Commercial Non-real Estate [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	776
Fiscal year before current fiscal year	536
Two years before current fiscal year	1,036
Three years before current fiscal year	1,051
Four years before current fiscal year	156
Prior	303
Revolving Loans Amortized Cost Basis	325
Total Loans	4,183
Commercial Non-real Estate [Member] | Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
Two years before current fiscal year	6
Three years before current fiscal year	175
Four years before current fiscal year	3
Prior	125
Total Loans	309
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	119,972
Fiscal year before current fiscal year	157,235
Two years before current fiscal year	95,563
Three years before current fiscal year	46,534
Four years before current fiscal year	20,450
Prior	7,982
Revolving Loans Amortized Cost Basis	33,989
Total Loans	481,725	478,647
Consumer Non-real Estate [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	105,760
Fiscal year before current fiscal year	138,858
Two years before current fiscal year	80,119
Three years before current fiscal year	37,879
Four years before current fiscal year	16,468
Prior	6,264
Revolving Loans Amortized Cost Basis	19,337
Total Loans	404,685
Consumer Non-real Estate [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	11,788
Fiscal year before current fiscal year	16,246
Two years before current fiscal year	12,780
Three years before current fiscal year	7,176
Four years before current fiscal year	3,127
Prior	1,331
Revolving Loans Amortized Cost Basis	14,638
Total Loans	67,086
Consumer Non-real Estate [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	591
Fiscal year before current fiscal year	1,408
Two years before current fiscal year	1,983
Three years before current fiscal year	985
Four years before current fiscal year	613
Prior	275
Revolving Loans Amortized Cost Basis	13
Total Loans	5,868
Consumer Non-real Estate [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,833
Fiscal year before current fiscal year	723
Two years before current fiscal year	681
Three years before current fiscal year	494
Four years before current fiscal year	242
Prior	112
Revolving Loans Amortized Cost Basis	1
Total Loans	4,086
Oil and Gas [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	109,553
Fiscal year before current fiscal year	23,459
Two years before current fiscal year	16,629
Three years before current fiscal year	7,472
Four years before current fiscal year	20,096
Prior	6,154
Revolving Loans Amortized Cost Basis	288,742
Total Loans	472,105	$ 509,858
Oil and Gas [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	71,743
Fiscal year before current fiscal year	14,587
Two years before current fiscal year	10,006
Three years before current fiscal year	3,822
Four years before current fiscal year	17,204
Prior	2,878
Revolving Loans Amortized Cost Basis	248,947
Total Loans	369,187
Oil and Gas [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	37,339
Fiscal year before current fiscal year	8,812
Two years before current fiscal year	6,555
Three years before current fiscal year	3,650
Four years before current fiscal year	2,675
Prior	2,818
Revolving Loans Amortized Cost Basis	39,275
Total Loans	101,124
Oil and Gas [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	471
Fiscal year before current fiscal year	60
Two years before current fiscal year	68
Four years before current fiscal year	159
Prior	50
Revolving Loans Amortized Cost Basis	520
Total Loans	1,328
Oil and Gas [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Four years before current fiscal year	58
Prior	408
Total Loans	$ 466