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	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	$ 575,035
Fiscal year before current fiscal year	1,935,478
Two years before current fiscal year	1,525,653
Three years before current fiscal year	1,050,103
Four years before current fiscal year	528,174
Prior	935,167
Revolving Loans Amortized Cost Basis	1,232,250
Total Loans	7,781,860	$ 7,656,645
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	35,372
Fiscal year before current fiscal year	151,687
Two years before current fiscal year	209,226
Three years before current fiscal year	166,981
Four years before current fiscal year	105,630
Prior	249,178
Revolving Loans Amortized Cost Basis	44,129
Total Loans	962,203	960,944
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	25,173
Fiscal year before current fiscal year	109,028
Two years before current fiscal year	159,208
Three years before current fiscal year	116,637
Four years before current fiscal year	82,223
Prior	203,263
Revolving Loans Amortized Cost Basis	18,941
Total Loans	714,473
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	6,168
Fiscal year before current fiscal year	34,656
Two years before current fiscal year	46,355
Three years before current fiscal year	44,871
Four years before current fiscal year	22,165
Prior	40,867
Revolving Loans Amortized Cost Basis	22,938
Total Loans	218,020
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	4,031
Fiscal year before current fiscal year	7,629
Two years before current fiscal year	3,640
Three years before current fiscal year	5,303
Four years before current fiscal year	890
Prior	3,055
Revolving Loans Amortized Cost Basis	2,100
Total Loans	26,648
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	374
Two years before current fiscal year	23
Three years before current fiscal year	170
Four years before current fiscal year	352
Prior	1,654
Revolving Loans Amortized Cost Basis	150
Total Loans	2,723
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
Prior	339
Total Loans	339
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	49,644
Fiscal year before current fiscal year	383,359
Two years before current fiscal year	411,814
Three years before current fiscal year	275,294
Four years before current fiscal year	161,886
Prior	213,923
Revolving Loans Amortized Cost Basis	35,265
Total Loans	1,531,185	1,486,420
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	30,431
Fiscal year before current fiscal year	217,786
Two years before current fiscal year	266,193
Three years before current fiscal year	187,861
Four years before current fiscal year	116,004
Prior	120,132
Revolving Loans Amortized Cost Basis	32,534
Total Loans	970,941
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	13,104
Fiscal year before current fiscal year	163,293
Two years before current fiscal year	144,208
Three years before current fiscal year	85,378
Four years before current fiscal year	45,784
Prior	93,020
Revolving Loans Amortized Cost Basis	2,731
Total Loans	547,518
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	6,109
Two years before current fiscal year	781
Three years before current fiscal year	1,703
Prior	247
Total Loans	8,840
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	2,280
Two years before current fiscal year	632
Three years before current fiscal year	352
Four years before current fiscal year	98
Prior	524
Total Loans	3,886
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	53,814
Fiscal year before current fiscal year	222,170
Two years before current fiscal year	211,581
Three years before current fiscal year	76,514
Four years before current fiscal year	12,025
Prior	23,220
Revolving Loans Amortized Cost Basis	70,402
Total Loans	669,726	642,643
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	29,037
Fiscal year before current fiscal year	89,815
Two years before current fiscal year	147,644
Three years before current fiscal year	50,050
Four years before current fiscal year	5,324
Prior	7,984
Revolving Loans Amortized Cost Basis	42,282
Total Loans	372,136
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	24,777
Fiscal year before current fiscal year	126,003
Two years before current fiscal year	62,244
Three years before current fiscal year	26,007
Four years before current fiscal year	6,561
Prior	15,166
Revolving Loans Amortized Cost Basis	8,778
Total Loans	269,536
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	6,352
Two years before current fiscal year	893
Three years before current fiscal year	357
Prior	70
Revolving Loans Amortized Cost Basis	19,342
Total Loans	27,014
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Two years before current fiscal year	800
Three years before current fiscal year	100
Four years before current fiscal year	140
Total Loans	1,040
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	63,670
Fiscal year before current fiscal year	151,384
Two years before current fiscal year	16,966
Three years before current fiscal year	8,641
Four years before current fiscal year	111
Prior	559
Revolving Loans Amortized Cost Basis	39,355
Total Loans	280,686	283,486
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	34,249
Fiscal year before current fiscal year	84,861
Two years before current fiscal year	14,251
Three years before current fiscal year	8,620
Four years before current fiscal year	99
Prior	559
Revolving Loans Amortized Cost Basis	38,050
Total Loans	180,689
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	28,843
Fiscal year before current fiscal year	58,132
Two years before current fiscal year	2,135
Three years before current fiscal year	21
Four years before current fiscal year	12
Prior	0
Revolving Loans Amortized Cost Basis	1,305
Total Loans	90,448
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	8,191
Two years before current fiscal year	374
Total Loans	8,565
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	578
Fiscal year before current fiscal year	200
Two years before current fiscal year	206
Total Loans	984
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	87,310
Fiscal year before current fiscal year	321,804
Two years before current fiscal year	259,974
Three years before current fiscal year	208,482
Four years before current fiscal year	138,001
Prior	263,671
Revolving Loans Amortized Cost Basis	4,637
Total Loans	1,283,879	1,258,744
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	72,174
Fiscal year before current fiscal year	268,280
Two years before current fiscal year	214,401
Three years before current fiscal year	167,456
Four years before current fiscal year	110,847
Prior	204,350
Revolving Loans Amortized Cost Basis	4,637
Total Loans	1,042,145
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	14,813
Fiscal year before current fiscal year	49,624
Two years before current fiscal year	42,664
Three years before current fiscal year	37,763
Four years before current fiscal year	24,732
Prior	51,823
Total Loans	221,419
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	232
Fiscal year before current fiscal year	2,987
Two years before current fiscal year	2,691
Three years before current fiscal year	2,538
Four years before current fiscal year	1,710
Prior	5,622
Total Loans	15,780
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	91
Fiscal year before current fiscal year	913
Two years before current fiscal year	218
Three years before current fiscal year	725
Four years before current fiscal year	712
Prior	1,876
Total Loans	4,535
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	10,395
Fiscal year before current fiscal year	41,757
Two years before current fiscal year	27,040
Three years before current fiscal year	8,522
Four years before current fiscal year	9,346
Prior	18,776
Revolving Loans Amortized Cost Basis	136,799
Total Loans	252,635	244,696
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	8,258
Fiscal year before current fiscal year	36,264
Two years before current fiscal year	21,550
Three years before current fiscal year	6,892
Four years before current fiscal year	7,585
Prior	14,383
Revolving Loans Amortized Cost Basis	55,776
Total Loans	150,708
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,682
Fiscal year before current fiscal year	5,082
Two years before current fiscal year	5,290
Three years before current fiscal year	1,434
Four years before current fiscal year	1,595
Prior	3,611
Revolving Loans Amortized Cost Basis	78,539
Total Loans	97,233
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	455
Fiscal year before current fiscal year	292
Two years before current fiscal year	176
Three years before current fiscal year	196
Four years before current fiscal year	166
Prior	671
Revolving Loans Amortized Cost Basis	1,590
Total Loans	3,546
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	119
Two years before current fiscal year	24
Three years before current fiscal year	0
Prior	111
Revolving Loans Amortized Cost Basis	894
Total Loans	1,148
Real Estate [Member] | Agriculture [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	26,903
Fiscal year before current fiscal year	92,297
Two years before current fiscal year	69,896
Three years before current fiscal year	51,907
Four years before current fiscal year	37,329
Prior	72,380
Revolving Loans Amortized Cost Basis	99,100
Total Loans	449,812	427,139
Real Estate [Member] | Agriculture [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	13,547
Fiscal year before current fiscal year	57,413
Two years before current fiscal year	47,429
Three years before current fiscal year	33,676
Four years before current fiscal year	25,336
Prior	48,773
Revolving Loans Amortized Cost Basis	49,003
Total Loans	275,177
Real Estate [Member] | Agriculture [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	11,754
Fiscal year before current fiscal year	25,588
Two years before current fiscal year	21,021
Three years before current fiscal year	17,212
Four years before current fiscal year	9,303
Prior	20,012
Revolving Loans Amortized Cost Basis	48,165
Total Loans	153,055
Real Estate [Member] | Agriculture [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,602
Fiscal year before current fiscal year	8,528
Two years before current fiscal year	819
Three years before current fiscal year	966
Four years before current fiscal year	2,591
Prior	3,328
Revolving Loans Amortized Cost Basis	1,931
Total Loans	19,765
Real Estate [Member] | Agriculture [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	768
Two years before current fiscal year	627
Three years before current fiscal year	53
Four years before current fiscal year	99
Prior	267
Revolving Loans Amortized Cost Basis	1
Total Loans	1,815
Commercial Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	63,861
Fiscal year before current fiscal year	285,964
Two years before current fiscal year	200,777
Three years before current fiscal year	167,663
Four years before current fiscal year	40,006
Prior	78,348
Revolving Loans Amortized Cost Basis	484,221
Total Loans	1,320,840	1,289,452
Commercial Non-real Estate [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	38,088
Fiscal year before current fiscal year	177,037
Two years before current fiscal year	163,957
Three years before current fiscal year	148,673
Four years before current fiscal year	32,770
Prior	64,198
Revolving Loans Amortized Cost Basis	317,586
Total Loans	942,309
Commercial Non-real Estate [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	24,463
Fiscal year before current fiscal year	106,857
Two years before current fiscal year	33,066
Three years before current fiscal year	17,747
Four years before current fiscal year	6,480
Prior	13,144
Revolving Loans Amortized Cost Basis	161,984
Total Loans	363,741
Commercial Non-real Estate [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,184
Fiscal year before current fiscal year	1,930
Two years before current fiscal year	2,260
Three years before current fiscal year	1,015
Four years before current fiscal year	283
Prior	196
Revolving Loans Amortized Cost Basis	3,411
Total Loans	10,279
Commercial Non-real Estate [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	126
Fiscal year before current fiscal year	122
Two years before current fiscal year	1,494
Three years before current fiscal year	228
Four years before current fiscal year	473
Prior	360
Revolving Loans Amortized Cost Basis	1,240
Total Loans	4,043
Commercial Non-real Estate [Member] | Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	18
Four years before current fiscal year	0
Prior	450
Total Loans	468
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	57,750
Fiscal year before current fiscal year	201,299
Two years before current fiscal year	106,895
Three years before current fiscal year	56,898
Four years before current fiscal year	17,282
Prior	11,089
Revolving Loans Amortized Cost Basis	13,953
Total Loans	465,166	476,467
Consumer Non-real Estate [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	52,889
Fiscal year before current fiscal year	180,937
Two years before current fiscal year	90,786
Three years before current fiscal year	49,021
Four years before current fiscal year	14,926
Prior	9,321
Revolving Loans Amortized Cost Basis	11,638
Total Loans	409,518
Consumer Non-real Estate [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	4,202
Fiscal year before current fiscal year	18,228
Two years before current fiscal year	14,005
Three years before current fiscal year	6,266
Four years before current fiscal year	1,906
Prior	1,323
Revolving Loans Amortized Cost Basis	2,299
Total Loans	48,229
Consumer Non-real Estate [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	565
Fiscal year before current fiscal year	1,714
Two years before current fiscal year	1,493
Three years before current fiscal year	1,221
Four years before current fiscal year	295
Prior	360
Revolving Loans Amortized Cost Basis	10
Total Loans	5,658
Consumer Non-real Estate [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	94
Fiscal year before current fiscal year	420
Two years before current fiscal year	611
Three years before current fiscal year	390
Four years before current fiscal year	155
Prior	85
Revolving Loans Amortized Cost Basis	6
Total Loans	1,761
Oil and Gas [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	126,316
Fiscal year before current fiscal year	83,757
Two years before current fiscal year	11,484
Three years before current fiscal year	29,201
Four years before current fiscal year	6,558
Prior	4,023
Revolving Loans Amortized Cost Basis	304,389
Total Loans	565,728	$ 586,654
Oil and Gas [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	70,735
Fiscal year before current fiscal year	71,998
Two years before current fiscal year	6,206
Three years before current fiscal year	28,039
Four years before current fiscal year	6,172
Prior	3,205
Revolving Loans Amortized Cost Basis	252,952
Total Loans	439,307
Oil and Gas [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	55,581
Fiscal year before current fiscal year	11,759
Two years before current fiscal year	5,278
Three years before current fiscal year	829
Four years before current fiscal year	386
Prior	358
Revolving Loans Amortized Cost Basis	51,437
Total Loans	125,628
Oil and Gas [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Three years before current fiscal year	185
Total Loans	185
Oil and Gas [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Three years before current fiscal year	148
Prior	460
Total Loans	$ 608