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, 2023	Dec. 31, 2022
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	$ 614,527
Fiscal year before current fiscal year	2,049,307
Two years before current fiscal year	1,322,022
Three years before current fiscal year	713,171
Four years before current fiscal year	521,371
Prior	783,261
Revolving Loans Amortized Cost Basis	1,114,949
Total loans	7,118,608	$ 6,943,563
Fiscal year before current fiscal year gross charge-offs	158
Two years before current fiscal year gross charge-offs	114
Three years before current fiscal year gross charge-offs	53
Four years before current fiscal year gross charge-offs	41
Prior gross charge-offs	64
Revolving Loans Amortized Cost Basis gross charge-offs	2
Current-period gross charge-offs	432
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	42,191
Fiscal year before current fiscal year	209,422
Two years before current fiscal year	171,573
Three years before current fiscal year	124,667
Four years before current fiscal year	109,694
Prior	192,973
Revolving Loans Amortized Cost Basis	69,584
Total loans	920,104	908,494
Fiscal year before current fiscal year gross charge-offs	7
Two years before current fiscal year gross charge-offs	1
Three years before current fiscal year gross charge-offs	22
Four years before current fiscal year gross charge-offs	18
Current-period gross charge-offs	48
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	26,840
Fiscal year before current fiscal year	171,896
Two years before current fiscal year	136,273
Three years before current fiscal year	98,471
Four years before current fiscal year	87,267
Prior	158,659
Revolving Loans Amortized Cost Basis	50,504
Total loans	729,910
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	15,333
Fiscal year before current fiscal year	37,268
Two years before current fiscal year	33,356
Three years before current fiscal year	25,810
Four years before current fiscal year	20,013
Prior	32,197
Revolving Loans Amortized Cost Basis	19,018
Total loans	182,995
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	18
Fiscal year before current fiscal year	6
Two years before current fiscal year	1,694
Three years before current fiscal year	75
Four years before current fiscal year	1,277
Prior	1,469
Revolving Loans Amortized Cost Basis	62
Total loans	4,601
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	252
Two years before current fiscal year	250
Three years before current fiscal year	311
Four years before current fiscal year	798
Prior	648
Total loans	2,259
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	53,529
Fiscal year before current fiscal year	464,090
Two years before current fiscal year	288,728
Three years before current fiscal year	193,773
Four years before current fiscal year	153,209
Prior	167,433
Revolving Loans Amortized Cost Basis	75,638
Total loans	1,396,400	1,383,150
Prior gross charge-offs	3
Current-period gross charge-offs	3
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	40,007
Fiscal year before current fiscal year	333,790
Two years before current fiscal year	239,906
Three years before current fiscal year	164,977
Four years before current fiscal year	106,365
Prior	86,491
Revolving Loans Amortized Cost Basis	44,389
Total loans	1,015,925
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	13,477
Fiscal year before current fiscal year	122,684
Two years before current fiscal year	48,822
Three years before current fiscal year	28,644
Four years before current fiscal year	36,980
Prior	79,557
Revolving Loans Amortized Cost Basis	31,249
Total loans	361,413
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	6,996
Three years before current fiscal year	152
Four years before current fiscal year	9,864
Prior	1,343
Total loans	18,355
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	45
Fiscal year before current fiscal year	620
Prior	42
Total loans	707
Real Estate [Member] \| Construction and Development Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	50,741
Fiscal year before current fiscal year	204,522
Two years before current fiscal year	97,199
Three years before current fiscal year	47,055
Four years before current fiscal year	19,148
Prior	9,354
Revolving Loans Amortized Cost Basis	106,828
Total loans	534,847	475,236
Fiscal year before current fiscal year gross charge-offs	2
Current-period gross charge-offs	2
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	44,459
Fiscal year before current fiscal year	152,820
Two years before current fiscal year	80,373
Three years before current fiscal year	39,720
Four years before current fiscal year	5,063
Prior	6,975
Revolving Loans Amortized Cost Basis	51,743
Total loans	381,153
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	3,757
Fiscal year before current fiscal year	50,735
Two years before current fiscal year	16,826
Three years before current fiscal year	7,203
Four years before current fiscal year	14,085
Prior	2,372
Revolving Loans Amortized Cost Basis	54,929
Total loans	149,907
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	2,525
Fiscal year before current fiscal year	886
Three years before current fiscal year	99
Prior	7
Revolving Loans Amortized Cost Basis	156
Total loans	3,673
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	81
Three years before current fiscal year	33
Total loans	114
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	68,235
Fiscal year before current fiscal year	193,401
Two years before current fiscal year	4,750
Three years before current fiscal year	304
Four years before current fiscal year	13
Prior	433
Revolving Loans Amortized Cost Basis	37,630
Total loans	304,766	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	59,006
Fiscal year before current fiscal year	156,832
Two years before current fiscal year	4,707
Three years before current fiscal year	258
Four years before current fiscal year	13
Prior	39
Revolving Loans Amortized Cost Basis	35,474
Total loans	256,329
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	8,841
Fiscal year before current fiscal year	35,304
Two years before current fiscal year	43
Three years before current fiscal year	46
Prior	394
Revolving Loans Amortized Cost Basis	2,156
Total loans	46,784
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	1,265
Total loans	1,265
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	388
Total loans	388
Real Estate [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	86,828
Fiscal year before current fiscal year	327,013
Two years before current fiscal year	235,796
Three years before current fiscal year	162,190
Four years before current fiscal year	97,518
Prior	232,762
Revolving Loans Amortized Cost Basis	5,693
Total loans	1,147,800	1,117,899
Prior gross charge-offs	2
Current-period gross charge-offs	2
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	77,619
Fiscal year before current fiscal year	281,309
Two years before current fiscal year	197,623
Three years before current fiscal year	135,722
Four years before current fiscal year	82,252
Prior	180,597
Revolving Loans Amortized Cost Basis	5,693
Total loans	960,815
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	8,715
Fiscal year before current fiscal year	43,684
Two years before current fiscal year	35,764
Three years before current fiscal year	25,194
Four years before current fiscal year	13,434
Prior	46,291
Total loans	173,082
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	428
Fiscal year before current fiscal year	1,910
Two years before current fiscal year	1,254
Three years before current fiscal year	905
Four years before current fiscal year	1,587
Prior	3,937
Total loans	10,021
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	66
Fiscal year before current fiscal year	110
Two years before current fiscal year	1,155
Three years before current fiscal year	369
Four years before current fiscal year	245
Prior	1,937
Total loans	3,882
Real Estate [Member] \| Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	9,541
Fiscal year before current fiscal year	36,654
Two years before current fiscal year	12,009
Three years before current fiscal year	11,688
Four years before current fiscal year	6,683
Prior	19,059
Revolving Loans Amortized Cost Basis	110,768
Total loans	206,402	196,198
Fiscal year before current fiscal year gross charge-offs	2
Two years before current fiscal year gross charge-offs	19
Four years before current fiscal year gross charge-offs	1
Prior gross charge-offs	4
Current-period gross charge-offs	26
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	8,382
Fiscal year before current fiscal year	30,718
Two years before current fiscal year	9,868
Three years before current fiscal year	9,884
Four years before current fiscal year	5,061
Prior	14,304
Revolving Loans Amortized Cost Basis	41,871
Total loans	120,088
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	987
Fiscal year before current fiscal year	5,712
Two years before current fiscal year	2,002
Three years before current fiscal year	1,729
Four years before current fiscal year	1,500
Prior	3,624
Revolving Loans Amortized Cost Basis	66,883
Total loans	82,437
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	172
Fiscal year before current fiscal year	224
Two years before current fiscal year	139
Three years before current fiscal year	48
Four years before current fiscal year	122
Prior	1,113
Revolving Loans Amortized Cost Basis	1,242
Total loans	3,060
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Three years before current fiscal year	27
Prior	18
Revolving Loans Amortized Cost Basis	772
Total loans	817
Real Estate [Member] \| Agriculture [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	28,037
Fiscal year before current fiscal year	101,114
Two years before current fiscal year	64,557
Three years before current fiscal year	47,505
Four years before current fiscal year	30,989
Prior	62,872
Revolving Loans Amortized Cost Basis	87,414
Total loans	422,488	408,037
Fiscal year before current fiscal year gross charge-offs	4
Three years before current fiscal year gross charge-offs	16
Four years before current fiscal year gross charge-offs	13
Prior gross charge-offs	2
Current-period gross charge-offs	35
Real Estate [Member] \| Agriculture [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	16,685
Fiscal year before current fiscal year	69,811
Two years before current fiscal year	42,014
Three years before current fiscal year	34,467
Four years before current fiscal year	20,604
Prior	39,693
Revolving Loans Amortized Cost Basis	49,791
Total loans	273,065
Real Estate [Member] \| Agriculture [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	10,701
Fiscal year before current fiscal year	24,320
Two years before current fiscal year	21,468
Three years before current fiscal year	9,205
Four years before current fiscal year	10,223
Prior	19,584
Revolving Loans Amortized Cost Basis	32,697
Total loans	128,198
Real Estate [Member] \| Agriculture [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	592
Fiscal year before current fiscal year	6,337
Two years before current fiscal year	977
Three years before current fiscal year	3,356
Four years before current fiscal year	112
Prior	3,290
Revolving Loans Amortized Cost Basis	4,896
Total loans	19,560
Real Estate [Member] \| Agriculture [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	59
Fiscal year before current fiscal year	646
Two years before current fiscal year	98
Three years before current fiscal year	477
Four years before current fiscal year	50
Prior	305
Revolving Loans Amortized Cost Basis	30
Total loans	1,665
Commercial Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	132,138
Fiscal year before current fiscal year	289,141
Two years before current fiscal year	232,806
Three years before current fiscal year	75,357
Four years before current fiscal year	59,896
Prior	71,002
Revolving Loans Amortized Cost Basis	402,397
Total loans	1,262,737	1,241,454
Fiscal year before current fiscal year gross charge-offs	67
Two years before current fiscal year gross charge-offs	62
Prior gross charge-offs	47
Current-period gross charge-offs	176
Commercial Non-real Estate [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	108,823
Fiscal year before current fiscal year	212,982
Two years before current fiscal year	189,496
Three years before current fiscal year	58,782
Four years before current fiscal year	45,803
Prior	47,346
Revolving Loans Amortized Cost Basis	305,503
Total loans	968,735
Commercial Non-real Estate [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	22,343
Fiscal year before current fiscal year	73,851
Two years before current fiscal year	42,567
Three years before current fiscal year	15,526
Four years before current fiscal year	12,546
Prior	21,578
Revolving Loans Amortized Cost Basis	94,656
Total loans	283,067
Commercial Non-real Estate [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	952
Fiscal year before current fiscal year	2,000
Two years before current fiscal year	392
Three years before current fiscal year	308
Four years before current fiscal year	675
Prior	1,773
Revolving Loans Amortized Cost Basis	2,035
Total loans	8,135
Commercial Non-real Estate [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	20
Fiscal year before current fiscal year	308
Two years before current fiscal year	351
Three years before current fiscal year	741
Four years before current fiscal year	608
Prior	305
Revolving Loans Amortized Cost Basis	203
Total loans	2,536
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	60,430
Fiscal year before current fiscal year	194,451
Two years before current fiscal year	100,392
Three years before current fiscal year	37,238
Four years before current fiscal year	18,939
Prior	8,933
Revolving Loans Amortized Cost Basis	21,114
Total loans	441,497	446,756
Fiscal year before current fiscal year gross charge-offs	76
Two years before current fiscal year gross charge-offs	32
Three years before current fiscal year gross charge-offs	15
Four years before current fiscal year gross charge-offs	9
Prior gross charge-offs	6
Revolving Loans Amortized Cost Basis gross charge-offs	2
Current-period gross charge-offs	140
Consumer Non-real Estate [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	56,874
Fiscal year before current fiscal year	174,237
Two years before current fiscal year	89,897
Three years before current fiscal year	33,413
Four years before current fiscal year	17,326
Prior	6,763
Revolving Loans Amortized Cost Basis	19,788
Total loans	398,298
Consumer Non-real Estate [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	3,455
Fiscal year before current fiscal year	19,044
Two years before current fiscal year	9,375
Three years before current fiscal year	3,409
Four years before current fiscal year	1,301
Prior	1,961
Revolving Loans Amortized Cost Basis	1,156
Total loans	39,701
Consumer Non-real Estate [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	101
Fiscal year before current fiscal year	831
Two years before current fiscal year	738
Three years before current fiscal year	372
Four years before current fiscal year	152
Prior	149
Revolving Loans Amortized Cost Basis	170
Total loans	2,513
Consumer Non-real Estate [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	339
Two years before current fiscal year	382
Three years before current fiscal year	44
Four years before current fiscal year	160
Prior	60
Total loans	985
Oil and Gas [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	82,857
Fiscal year before current fiscal year	29,499
Two years before current fiscal year	114,212
Three years before current fiscal year	13,394
Four years before current fiscal year	25,282
Prior	18,440
Revolving Loans Amortized Cost Basis	197,883
Total loans	481,567	$ 463,034
Oil and Gas [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	81,777
Fiscal year before current fiscal year	21,451
Two years before current fiscal year	110,461
Three years before current fiscal year	12,661
Four years before current fiscal year	3,861
Prior	2,469
Revolving Loans Amortized Cost Basis	167,211
Total loans	399,891
Oil and Gas [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,080
Fiscal year before current fiscal year	5,968
Two years before current fiscal year	3,504
Three years before current fiscal year	729
Four years before current fiscal year	21,421
Prior	15,971
Revolving Loans Amortized Cost Basis	29,233
Total loans	77,906
Oil and Gas [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]

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