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, 2022	Dec. 31, 2021
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	$ 1,856,792
Fiscal year before current fiscal year	1,545,836
Two years before current fiscal year	814,101
Three years before current fiscal year	568,089
Four years before current fiscal year	275,358
Prior	637,065
Revolving Loans Amortized Cost Basis	1,130,531
Total Loans	6,827,772	$ 6,169,442
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	172,545
Fiscal year before current fiscal year	182,383
Two years before current fiscal year	143,444
Three years before current fiscal year	114,850
Four years before current fiscal year	57,190
Prior	162,103
Revolving Loans Amortized Cost Basis	63,687
Total Loans	896,202	775,554
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	141,987
Fiscal year before current fiscal year	145,596
Two years before current fiscal year	114,356
Three years before current fiscal year	93,878
Four years before current fiscal year	47,340
Prior	129,610
Revolving Loans Amortized Cost Basis	48,189
Total Loans	720,956
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	30,513
Fiscal year before current fiscal year	36,392
Two years before current fiscal year	29,012
Three years before current fiscal year	18,542
Four years before current fiscal year	9,327
Prior	30,565
Revolving Loans Amortized Cost Basis	15,436
Total Loans	169,787
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	126
Two years before current fiscal year	76
Three years before current fiscal year	1,302
Four years before current fiscal year	337
Prior	1,421
Revolving Loans Amortized Cost Basis	62
Total Loans	3,324
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	45
Fiscal year before current fiscal year	269
Three years before current fiscal year	1,128
Four years before current fiscal year	186
Prior	507
Total Loans	2,135
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	293,303
Fiscal year before current fiscal year	294,647
Two years before current fiscal year	207,478
Three years before current fiscal year	159,304
Four years before current fiscal year	52,200
Prior	152,812
Revolving Loans Amortized Cost Basis	70,330
Total Loans	1,230,074	1,095,324
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	198,064
Fiscal year before current fiscal year	238,174
Two years before current fiscal year	177,410
Three years before current fiscal year	109,128
Four years before current fiscal year	26,907
Prior	77,085
Revolving Loans Amortized Cost Basis	39,667
Total Loans	866,435
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	88,113
Fiscal year before current fiscal year	56,473
Two years before current fiscal year	30,068
Three years before current fiscal year	47,428
Four years before current fiscal year	25,178
Prior	72,943
Revolving Loans Amortized Cost Basis	30,663
Total Loans	350,866
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	7,126
Three years before current fiscal year	2,748
Four years before current fiscal year	79
Prior	2,784
Total Loans	12,737
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Four years before current fiscal year	36
Total Loans	36
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	168,489
Fiscal year before current fiscal year	142,836
Two years before current fiscal year	43,391
Three years before current fiscal year	25,234
Four years before current fiscal year	5,219
Prior	6,743
Revolving Loans Amortized Cost Basis	81,719
Total Loans	473,631	415,466
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	138,067
Fiscal year before current fiscal year	122,780
Two years before current fiscal year	41,667
Three years before current fiscal year	10,473
Four years before current fiscal year	3,510
Prior	5,479
Revolving Loans Amortized Cost Basis	33,306
Total Loans	355,282
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	29,324
Fiscal year before current fiscal year	20,056
Two years before current fiscal year	1,589
Three years before current fiscal year	14,711
Four years before current fiscal year	1,709
Prior	1,249
Revolving Loans Amortized Cost Basis	48,254
Total Loans	116,892
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,098
Two years before current fiscal year	102
Revolving Loans Amortized Cost Basis	159
Total Loans	1,359
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	33
Three years before current fiscal year	50
Prior	15
Total Loans	98
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	205,704
Fiscal year before current fiscal year	55,721
Two years before current fiscal year	440
Three years before current fiscal year	22
Prior	450
Revolving Loans Amortized Cost Basis	48,831
Total Loans	311,168	254,524
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	178,568
Fiscal year before current fiscal year	47,012
Two years before current fiscal year	261
Three years before current fiscal year	22
Prior	43
Revolving Loans Amortized Cost Basis	46,695
Total Loans	272,601
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	26,903
Fiscal year before current fiscal year	8,606
Two years before current fiscal year	179
Prior	407
Revolving Loans Amortized Cost Basis	2,136
Total Loans	38,231
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	233
Total Loans	233
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	103
Total Loans	103
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	288,089
Fiscal year before current fiscal year	258,092
Two years before current fiscal year	176,748
Three years before current fiscal year	106,435
Four years before current fiscal year	71,473
Prior	191,951
Revolving Loans Amortized Cost Basis	4,922
Total Loans	1,097,710	937,006
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	251,829
Fiscal year before current fiscal year	218,962
Two years before current fiscal year	150,043
Three years before current fiscal year	90,854
Four years before current fiscal year	58,348
Prior	146,667
Revolving Loans Amortized Cost Basis	4,922
Total Loans	921,625
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	34,687
Fiscal year before current fiscal year	37,637
Two years before current fiscal year	25,916
Three years before current fiscal year	13,497
Four years before current fiscal year	11,075
Prior	39,349
Total Loans	162,161
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,543
Fiscal year before current fiscal year	1,171
Two years before current fiscal year	651
Three years before current fiscal year	1,516
Four years before current fiscal year	1,870
Prior	4,143
Total Loans	10,894
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	30
Fiscal year before current fiscal year	322
Two years before current fiscal year	138
Three years before current fiscal year	568
Four years before current fiscal year	180
Prior	1,792
Total Loans	3,030
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	28,874
Fiscal year before current fiscal year	13,637
Two years before current fiscal year	13,449
Three years before current fiscal year	7,700
Four years before current fiscal year	5,431
Prior	15,455
Revolving Loans Amortized Cost Basis	103,962
Total Loans	188,508	161,018
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	24,287
Fiscal year before current fiscal year	11,519
Two years before current fiscal year	11,471
Three years before current fiscal year	5,940
Four years before current fiscal year	3,909
Prior	11,865
Revolving Loans Amortized Cost Basis	41,165
Total Loans	110,156
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	4,387
Fiscal year before current fiscal year	1,896
Two years before current fiscal year	1,860
Three years before current fiscal year	1,676
Four years before current fiscal year	1,261
Prior	2,646
Revolving Loans Amortized Cost Basis	62,195
Total Loans	75,921
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	200
Fiscal year before current fiscal year	204
Two years before current fiscal year	88
Three years before current fiscal year	84
Four years before current fiscal year	222
Prior	890
Revolving Loans Amortized Cost Basis	602
Total Loans	2,290
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	18
Two years before current fiscal year	30
Four years before current fiscal year	39
Prior	54
Total Loans	141
Real Estate [Member] | Farmland [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	54,603
Fiscal year before current fiscal year	51,834
Two years before current fiscal year	39,552
Three years before current fiscal year	28,709
Four years before current fiscal year	16,260
Prior	49,097
Revolving Loans Amortized Cost Basis	16,766
Total Loans	256,821	272,179
Real Estate [Member] | Farmland [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	39,963
Fiscal year before current fiscal year	36,229
Two years before current fiscal year	30,416
Three years before current fiscal year	19,528
Four years before current fiscal year	10,297
Prior	30,735
Revolving Loans Amortized Cost Basis	5,256
Total Loans	172,424
Real Estate [Member] | Farmland [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	12,439
Fiscal year before current fiscal year	15,174
Two years before current fiscal year	6,903
Three years before current fiscal year	7,816
Four years before current fiscal year	5,835
Prior	16,093
Revolving Loans Amortized Cost Basis	9,619
Total Loans	73,879
Real Estate [Member] | Farmland [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	2,201
Fiscal year before current fiscal year	113
Two years before current fiscal year	1,799
Three years before current fiscal year	1,365
Four years before current fiscal year	70
Prior	2,057
Revolving Loans Amortized Cost Basis	1,891
Total Loans	9,496
Real Estate [Member] | Farmland [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	318
Two years before current fiscal year	434
Four years before current fiscal year	58
Prior	212
Total Loans	1,022
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	323,293
Fiscal year before current fiscal year	325,919
Two years before current fiscal year	109,960
Three years before current fiscal year	75,973
Four years before current fiscal year	36,896
Prior	53,191
Revolving Loans Amortized Cost Basis	504,169
Total Loans	1,429,401	1,416,093
Commercial and Agricultural Non-Real Estate [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	239,757
Fiscal year before current fiscal year	257,163
Two years before current fiscal year	83,658
Three years before current fiscal year	58,217
Four years before current fiscal year	17,413
Prior	46,390
Revolving Loans Amortized Cost Basis	361,517
Total Loans	1,064,115
Commercial and Agricultural Non-Real Estate [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	79,522
Fiscal year before current fiscal year	65,913
Two years before current fiscal year	23,868
Three years before current fiscal year	15,699
Four years before current fiscal year	17,090
Prior	4,710
Revolving Loans Amortized Cost Basis	136,388
Total Loans	343,190
Commercial and Agricultural Non-Real Estate [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	3,575
Fiscal year before current fiscal year	2,290
Two years before current fiscal year	1,843
Three years before current fiscal year	936
Four years before current fiscal year	1,896
Prior	932
Revolving Loans Amortized Cost Basis	6,094
Total Loans	17,566
Commercial and Agricultural Non-Real Estate [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	439
Fiscal year before current fiscal year	553
Two years before current fiscal year	591
Three years before current fiscal year	1,121
Four years before current fiscal year	497
Prior	1,159
Revolving Loans Amortized Cost Basis	170
Total Loans	4,530
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	180,129
Fiscal year before current fiscal year	134,462
Two years before current fiscal year	51,898
Three years before current fiscal year	29,343
Four years before current fiscal year	9,709
Prior	4,579
Revolving Loans Amortized Cost Basis	21,793
Total Loans	431,913	413,370
Consumer Non-real Estate [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	163,610
Fiscal year before current fiscal year	121,331
Two years before current fiscal year	46,856
Three years before current fiscal year	24,674
Four years before current fiscal year	8,419
Prior	2,989
Revolving Loans Amortized Cost Basis	20,821
Total Loans	388,700
Consumer Non-real Estate [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	15,625
Fiscal year before current fiscal year	12,007
Two years before current fiscal year	4,564
Three years before current fiscal year	4,113
Four years before current fiscal year	1,079
Prior	1,511
Revolving Loans Amortized Cost Basis	968
Total Loans	39,867
Consumer Non-real Estate [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	663
Fiscal year before current fiscal year	817
Two years before current fiscal year	370
Three years before current fiscal year	381
Four years before current fiscal year	159
Prior	67
Revolving Loans Amortized Cost Basis	3
Total Loans	2,460
Consumer Non-real Estate [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	231
Fiscal year before current fiscal year	307
Two years before current fiscal year	108
Three years before current fiscal year	175
Four years before current fiscal year	52
Prior	12
Revolving Loans Amortized Cost Basis	1
Total Loans	886
Oil and Gas [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	141,763
Fiscal year before current fiscal year	86,305
Two years before current fiscal year	27,741
Three years before current fiscal year	20,519
Four years before current fiscal year	20,980
Prior	684
Revolving Loans Amortized Cost Basis	214,352
Total Loans	512,344	$ 428,908
Oil and Gas [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	137,122
Fiscal year before current fiscal year	76,145
Two years before current fiscal year	24,844
Three years before current fiscal year	864
Four years before current fiscal year	1,732
Prior	313
Revolving Loans Amortized Cost Basis	175,742
Total Loans	416,762
Oil and Gas [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	4,432
Fiscal year before current fiscal year	4,603
Two years before current fiscal year	2,890
Three years before current fiscal year	19,655
Four years before current fiscal year	19,248
Prior	200
Revolving Loans Amortized Cost Basis	36,964
Total Loans	87,992
Oil and Gas [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	209
Fiscal year before current fiscal year	4,557
Two years before current fiscal year	7
Prior	171
Revolving Loans Amortized Cost Basis	1,646
Total Loans	6,590
Oil and Gas [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	1,000
Total Loans	$ 1,000