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, 2022	Dec. 31, 2021
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	$ 1,217,401
Fiscal year before current fiscal year	1,718,960
Two years before current fiscal year	892,016
Three years before current fiscal year	640,007
Four years before current fiscal year	320,149
Prior	740,053
Revolving Loans Amortized Cost Basis	1,084,697
Total Loans	6,613,283	$ 6,169,442
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	124,611
Fiscal year before current fiscal year	188,215
Two years before current fiscal year	152,400
Three years before current fiscal year	122,011
Four years before current fiscal year	60,524
Prior	173,838
Revolving Loans Amortized Cost Basis	71,545
Total Loans	893,144	775,554
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	98,837
Fiscal year before current fiscal year	153,898
Two years before current fiscal year	119,189
Three years before current fiscal year	98,981
Four years before current fiscal year	49,907
Prior	138,353
Revolving Loans Amortized Cost Basis	47,977
Total Loans	707,142
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	25,774
Fiscal year before current fiscal year	33,972
Two years before current fiscal year	32,759
Three years before current fiscal year	21,243
Four years before current fiscal year	10,083
Prior	33,359
Revolving Loans Amortized Cost Basis	23,049
Total Loans	180,239
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	42
Two years before current fiscal year	452
Three years before current fiscal year	936
Four years before current fiscal year	341
Prior	1,606
Revolving Loans Amortized Cost Basis	212
Total Loans	3,589
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	303
Three years before current fiscal year	851
Four years before current fiscal year	193
Prior	520
Revolving Loans Amortized Cost Basis	307
Total Loans	2,174
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	151,869
Fiscal year before current fiscal year	293,249
Two years before current fiscal year	229,779
Three years before current fiscal year	165,134
Four years before current fiscal year	71,456
Prior	193,346
Revolving Loans Amortized Cost Basis	58,079
Total Loans	1,162,912	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	86,546
Fiscal year before current fiscal year	238,973
Two years before current fiscal year	183,794
Three years before current fiscal year	112,077
Four years before current fiscal year	38,979
Prior	104,280
Revolving Loans Amortized Cost Basis	28,735
Total Loans	793,384
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	58,327
Fiscal year before current fiscal year	54,276
Two years before current fiscal year	45,985
Three years before current fiscal year	49,899
Four years before current fiscal year	32,181
Prior	86,252
Revolving Loans Amortized Cost Basis	29,344
Total Loans	356,264
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	6,996
Three years before current fiscal year	3,158
Four years before current fiscal year	93
Prior	2,814
Total Loans	13,061
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	203
Total Loans	203
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	79,463
Fiscal year before current fiscal year	164,309
Two years before current fiscal year	44,049
Three years before current fiscal year	52,701
Four years before current fiscal year	5,362
Prior	7,181
Revolving Loans Amortized Cost Basis	83,593
Total Loans	436,658	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	60,042
Fiscal year before current fiscal year	136,104
Two years before current fiscal year	42,114
Three years before current fiscal year	37,833
Four years before current fiscal year	3,629
Prior	5,887
Revolving Loans Amortized Cost Basis	40,046
Total Loans	325,655
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	18,223
Fiscal year before current fiscal year	28,205
Two years before current fiscal year	1,799
Three years before current fiscal year	14,816
Four years before current fiscal year	1,733
Prior	1,277
Revolving Loans Amortized Cost Basis	43,436
Total Loans	109,489
Real Estate [Member] | Construction and Development Less than 60 Months [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,198
Two years before current fiscal year	103
Prior	2
Revolving Loans Amortized Cost Basis	111
Total Loans	1,414
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	52
Prior	15
Total Loans	100
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	138,105
Fiscal year before current fiscal year	108,648
Two years before current fiscal year	4,168
Three years before current fiscal year	26
Prior	457
Revolving Loans Amortized Cost Basis	33,686
Total Loans	285,090	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	119,503
Fiscal year before current fiscal year	94,469
Two years before current fiscal year	3,821
Three years before current fiscal year	26
Prior	44
Revolving Loans Amortized Cost Basis	31,831
Total Loans	249,694
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	18,089
Fiscal year before current fiscal year	14,076
Two years before current fiscal year	347
Prior	413
Revolving Loans Amortized Cost Basis	1,855
Total Loans	34,780
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	513
Total Loans	513
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	206,518
Fiscal year before current fiscal year	274,984
Two years before current fiscal year	189,539
Three years before current fiscal year	110,969
Four years before current fiscal year	76,280
Prior	207,878
Revolving Loans Amortized Cost Basis	6,396
Total Loans	1,072,564	937,006
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	181,536
Fiscal year before current fiscal year	234,262
Two years before current fiscal year	162,322
Three years before current fiscal year	94,607
Four years before current fiscal year	61,203
Prior	157,490
Revolving Loans Amortized Cost Basis	6,396
Total Loans	897,816
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	23,461
Fiscal year before current fiscal year	39,031
Two years before current fiscal year	25,983
Three years before current fiscal year	14,136
Four years before current fiscal year	12,264
Prior	44,323
Total Loans	159,198
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,521
Fiscal year before current fiscal year	1,492
Two years before current fiscal year	1,050
Three years before current fiscal year	1,701
Four years before current fiscal year	1,826
Prior	3,800
Total Loans	11,390
Real Estate [Member] | Residential Real Estate First Lien [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	199
Two years before current fiscal year	184
Three years before current fiscal year	525
Four years before current fiscal year	987
Prior	2,265
Total Loans	4,160
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	19,083
Fiscal year before current fiscal year	15,112
Two years before current fiscal year	14,974
Three years before current fiscal year	8,664
Four years before current fiscal year	5,830
Prior	16,959
Revolving Loans Amortized Cost Basis	93,292
Total Loans	173,914	161,018
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	16,908
Fiscal year before current fiscal year	13,021
Two years before current fiscal year	12,762
Three years before current fiscal year	6,836
Four years before current fiscal year	4,343
Prior	13,031
Revolving Loans Amortized Cost Basis	33,925
Total Loans	100,826
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	1,990
Fiscal year before current fiscal year	1,849
Two years before current fiscal year	1,944
Three years before current fiscal year	1,761
Four years before current fiscal year	1,206
Prior	2,820
Revolving Loans Amortized Cost Basis	58,388
Total Loans	69,958
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	185
Fiscal year before current fiscal year	211
Two years before current fiscal year	91
Three years before current fiscal year	67
Four years before current fiscal year	243
Prior	890
Revolving Loans Amortized Cost Basis	589
Total Loans	2,276
Real Estate [Member] | Residential Real Estate All Other [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	31
Two years before current fiscal year	177
Four years before current fiscal year	38
Prior	218
Revolving Loans Amortized Cost Basis	390
Total Loans	854
Real Estate [Member] | Farmland [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	37,256
Fiscal year before current fiscal year	60,161
Two years before current fiscal year	42,658
Three years before current fiscal year	36,293
Four years before current fiscal year	17,213
Prior	52,231
Revolving Loans Amortized Cost Basis	20,978
Total Loans	266,790	272,179
Real Estate [Member] | Farmland [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	26,555
Fiscal year before current fiscal year	40,429
Two years before current fiscal year	32,947
Three years before current fiscal year	21,399
Four years before current fiscal year	11,001
Prior	32,232
Revolving Loans Amortized Cost Basis	6,702
Total Loans	171,265
Real Estate [Member] | Farmland [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	8,434
Fiscal year before current fiscal year	16,653
Two years before current fiscal year	7,470
Three years before current fiscal year	13,116
Four years before current fiscal year	6,084
Prior	17,368
Revolving Loans Amortized Cost Basis	12,121
Total Loans	81,246
Real Estate [Member] | Farmland [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	2,267
Fiscal year before current fiscal year	1,954
Two years before current fiscal year	1,862
Three years before current fiscal year	1,778
Four years before current fiscal year	70
Prior	2,409
Revolving Loans Amortized Cost Basis	1,923
Total Loans	12,263
Real Estate [Member] | Farmland [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	1,125
Two years before current fiscal year	379
Four years before current fiscal year	58
Prior	222
Revolving Loans Amortized Cost Basis	232
Total Loans	2,016
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	209,815
Fiscal year before current fiscal year	344,327
Two years before current fiscal year	131,116
Three years before current fiscal year	90,926
Four years before current fiscal year	51,494
Prior	81,278
Revolving Loans Amortized Cost Basis	490,746
Total Loans	1,399,702	1,416,093
Commercial and Agricultural Non-Real Estate [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	160,548
Fiscal year before current fiscal year	271,247
Two years before current fiscal year	100,081
Three years before current fiscal year	71,623
Four years before current fiscal year	22,808
Prior	71,498
Revolving Loans Amortized Cost Basis	337,631
Total Loans	1,035,436
Commercial and Agricultural Non-Real Estate [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	46,899
Fiscal year before current fiscal year	69,950
Two years before current fiscal year	28,657
Three years before current fiscal year	17,177
Four years before current fiscal year	26,250
Prior	7,737
Revolving Loans Amortized Cost Basis	145,827
Total Loans	342,497
Commercial and Agricultural Non-Real Estate [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	2,368
Fiscal year before current fiscal year	2,451
Two years before current fiscal year	2,144
Three years before current fiscal year	1,219
Four years before current fiscal year	1,937
Prior	806
Revolving Loans Amortized Cost Basis	7,019
Total Loans	17,944
Commercial and Agricultural Non-Real Estate [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	679
Two years before current fiscal year	234
Three years before current fiscal year	907
Four years before current fiscal year	499
Prior	1,237
Revolving Loans Amortized Cost Basis	269
Total Loans	3,825
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	126,315
Fiscal year before current fiscal year	156,861
Two years before current fiscal year	61,604
Three years before current fiscal year	35,234
Four years before current fiscal year	12,415
Prior	6,110
Revolving Loans Amortized Cost Basis	41,184
Total Loans	439,723	413,370
Consumer Non-real Estate [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	112,598
Fiscal year before current fiscal year	141,806
Two years before current fiscal year	55,814
Three years before current fiscal year	30,229
Four years before current fiscal year	10,829
Prior	3,970
Revolving Loans Amortized Cost Basis	35,949
Total Loans	391,195
Consumer Non-real Estate [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	13,357
Fiscal year before current fiscal year	14,002
Two years before current fiscal year	5,298
Three years before current fiscal year	4,529
Four years before current fiscal year	1,395
Prior	2,042
Revolving Loans Amortized Cost Basis	5,233
Total Loans	45,856
Consumer Non-real Estate [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	296
Fiscal year before current fiscal year	767
Two years before current fiscal year	405
Three years before current fiscal year	294
Four years before current fiscal year	127
Prior	97
Revolving Loans Amortized Cost Basis	2
Total Loans	1,988
Consumer Non-real Estate [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	64
Fiscal year before current fiscal year	286
Two years before current fiscal year	87
Three years before current fiscal year	182
Four years before current fiscal year	64
Prior	1
Total Loans	684
Oil and Gas [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	124,366
Fiscal year before current fiscal year	113,094
Two years before current fiscal year	21,729
Three years before current fiscal year	18,049
Four years before current fiscal year	19,575
Prior	775
Revolving Loans Amortized Cost Basis	185,198
Total Loans	482,786	$ 428,908
Oil and Gas [Member] | Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	115,020
Fiscal year before current fiscal year	101,947
Two years before current fiscal year	18,040
Three years before current fiscal year	4,468
Four years before current fiscal year	1,798
Prior	326
Revolving Loans Amortized Cost Basis	152,151
Total Loans	393,750
Oil and Gas [Member] | Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	9,301
Fiscal year before current fiscal year	5,414
Two years before current fiscal year	3,681
Three years before current fiscal year	13,581
Four years before current fiscal year	17,777
Prior	250
Revolving Loans Amortized Cost Basis	30,898
Total Loans	80,902
Oil and Gas [Member] | Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Current fiscal year	45
Fiscal year before current fiscal year	4,733
Two years before current fiscal year	8
Prior	199
Revolving Loans Amortized Cost Basis	2,080
Total Loans	7,065
Oil and Gas [Member] | Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Fiscal year before current fiscal year	1,000
Revolving Loans Amortized Cost Basis	69
Total Loans	$ 1,069