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, 2021	Dec. 31, 2020
Financing Receivable Recorded Investment [Line Items]
2021	$ 1,824,056
2020	1,197,631
2019	824,614
2018	412,040
2017	307,196
Prior	715,083
Revolving Loans Amortized Cost Basis	736,316
Total Loans	6,016,936	$ 6,394,506
Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
2021	153,237
2020	102,163
2019	72,012
2018	16,222
2017	36,819
Prior	42,703
Revolving Loans Amortized Cost Basis	195,532
Total Loans	618,688	554,548
Pegasus Bank [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	90,125
2020	92,819
2019	55,004
2018	5,023
2017	14,241
Prior	36,338
Revolving Loans Amortized Cost Basis	156,927
Total Loans	450,477
Pegasus Bank [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	62,861
2020	9,238
2019	17,008
2018	11,199
2017	22,578
Prior	6,365
Revolving Loans Amortized Cost Basis	38,605
Total Loans	167,854
Pegasus Bank [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	251
2020	106
Total Loans	357
Real Estate [Member] \| Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
Total Loans	339,000
Real Estate [Member] \| Farmland [Member]
Financing Receivable Recorded Investment [Line Items]
2021	57,919
2020	54,737
2019	50,420
2018	25,493
2017	18,758
Prior	45,536
Revolving Loans Amortized Cost Basis	17,352
Total Loans	270,215	252,958
Real Estate [Member] \| Farmland [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	41,033
2020	40,571
2019	24,326
2018	17,269
2017	13,249
Prior	31,871
Revolving Loans Amortized Cost Basis	5,473
Total Loans	173,792
Real Estate [Member] \| Farmland [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	13,328
2020	9,683
2019	24,655
2018	5,522
2017	4,069
Prior	12,184
Revolving Loans Amortized Cost Basis	9,628
Total Loans	79,069
Real Estate [Member] \| Farmland [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	2,785
2020	4,069
2019	1,439
2018	319
2017	1,330
Prior	1,272
Revolving Loans Amortized Cost Basis	1,973
Total Loans	13,187
Real Estate [Member] \| Farmland [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	773
2020	414
2018	2,383
2017	110
Prior	209
Revolving Loans Amortized Cost Basis	278
Total Loans	4,167
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
2021	114,339
2020	172,909
2019	101,601
2018	60,980
2017	44,730
Prior	138,984
Revolving Loans Amortized Cost Basis	19,816
Total Loans	653,359	641,987
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	89,910
2020	130,040
2019	78,492
2018	50,380
2017	34,793
Prior	98,825
Revolving Loans Amortized Cost Basis	11,514
Total Loans	493,954
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	24,092
2020	38,773
2019	22,069
2018	9,884
2017	9,466
Prior	38,454
Revolving Loans Amortized Cost Basis	7,977
Total Loans	150,715
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	0
2020	4,096
2019	129
2018	264
2017	471
Prior	1,374
Total Loans	6,334
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	337
2019	911
2018	452
Prior	331
Revolving Loans Amortized Cost Basis	325
Total Loans	2,356
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
2021	175,147
2020	265,190
2019	187,187
2018	92,660
2017	55,462
Prior	173,273
Revolving Loans Amortized Cost Basis	14,625
Total Loans	963,544	971,158
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	124,690
2020	210,442
2019	139,681
2018	58,198
2017	36,899
Prior	130,688
Revolving Loans Amortized Cost Basis	9,475
Total Loans	710,073
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	42,653
2020	54,748
2019	44,156
2018	34,292
2017	18,326
Prior	41,774
Revolving Loans Amortized Cost Basis	5,150
Total Loans	241,099
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	7,387
2019	3,301
2018	135
2017	237
Prior	642
Total Loans	11,702
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	417
2019	49
2018	35
Prior	169
Total Loans	670
Real Estate [Member] \| Construction and Development Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
2021	140,940
2020	47,364
2019	77,694
2018	13,193
2017	3,881
Prior	3,375
Revolving Loans Amortized Cost Basis	15,628
Total Loans	302,075	229,615
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	123,070
2020	37,650
2019	64,046
2018	11,080
2017	2,081
Prior	2,775
Revolving Loans Amortized Cost Basis	13,624
Total Loans	254,326
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	16,597
2020	9,714
2019	13,590
2018	2,099
2017	1,782
Prior	600
Revolving Loans Amortized Cost Basis	2,004
Total Loans	46,386
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	1,273
2020	0
2019	0
2018	7
Total Loans	1,280
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2019	58
2018	7
2017	18
Total Loans	83
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
2021	178,454
2020	47,986
2019	46
2018	107
2017	19
Prior	460
Revolving Loans Amortized Cost Basis	222
Total Loans	227,294	206,195
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	156,524
2020	38,426
2019	46
2017	19
Prior	29
Revolving Loans Amortized Cost Basis	222
Total Loans	195,266
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	21,383
2020	9,425
2018	107
Prior	431
Total Loans	31,346
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	547
2020	135
Total Loans	682
Real Estate [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable Recorded Investment [Line Items]
2021	227,907
2020	196,672
2019	120,220
2018	84,069
2017	59,959
Prior	188,333
Total Loans	877,160	853,316
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	193,151
2020	168,628
2019	100,936
2018	64,930
2017	47,968
Prior	141,503
Total Loans	717,116
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	33,765
2020	25,873
2019	16,379
2018	15,931
2017	9,710
Prior	40,834
Total Loans	142,492
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	942
2020	1,523
2019	2,375
2018	2,044
2017	1,350
Prior	4,391
Total Loans	12,625
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	49
2020	648
2019	530
2018	1,164
2017	931
Prior	1,605
Total Loans	4,927
Real Estate [Member] \| Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
2021	14,446
2020	17,506
2019	12,003
2018	8,764
2017	5,839
Prior	16,598
Revolving Loans Amortized Cost Basis	82,989
Total Loans	158,145	168,081
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	12,798
2020	14,033
2019	9,976
2018	6,381
2017	4,203
Prior	13,338
Revolving Loans Amortized Cost Basis	27,591
Total Loans	88,320
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	1,355
2020	3,188
2019	1,763
2018	1,563
2017	914
Prior	2,284
Revolving Loans Amortized Cost Basis	54,473
Total Loans	65,540
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	279
2020	102
2019	264
2018	240
2017	709
Prior	327
Revolving Loans Amortized Cost Basis	556
Total Loans	2,477
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	14
2020	183
2018	580
2017	13
Prior	649
Revolving Loans Amortized Cost Basis	369
Total Loans	1,808
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
2021	281,508
2020	154,515
2019	122,146
2018	69,204
2017	55,869
Prior	63,780
Revolving Loans Amortized Cost Basis	318,951
Total Loans	1,065,973	1,159,810
Commercial and Agricultural Non-Real Estate [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	222,156
2020	110,551
2019	93,150
2018	46,932
2017	50,431
Prior	48,206
Revolving Loans Amortized Cost Basis	216,301
Total Loans	787,727
Commercial and Agricultural Non-Real Estate [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	52,100
2020	37,867
2019	26,032
2018	9,759
2017	3,176
Prior	13,683
Revolving Loans Amortized Cost Basis	72,080
Total Loans	214,697
Commercial and Agricultural Non-Real Estate [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	4,577
2020	5,676
2019	1,357
2018	11,555
2017	1,452
Prior	623
Revolving Loans Amortized Cost Basis	28,105
Total Loans	53,345
Commercial and Agricultural Non-Real Estate [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	2,675
2020	421
2019	1,607
2018	958
2017	810
Prior	1,268
Revolving Loans Amortized Cost Basis	2,465
Total Loans	10,204
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
2021	177,675
2020	105,176
2019	57,632
2018	24,534
2017	8,533
Prior	4,545
Revolving Loans Amortized Cost Basis	5,783
Total Loans	383,878	355,405
Consumer Non-real Estate [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	162,782
2020	96,567
2019	52,943
2018	22,050
2017	7,474
Prior	3,033
Revolving Loans Amortized Cost Basis	5,483
Total Loans	350,332
Consumer Non-real Estate [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	14,402
2020	8,211
2019	3,850
2018	2,083
2017	958
Prior	1,450
Revolving Loans Amortized Cost Basis	295
Total Loans	31,249
Consumer Non-real Estate [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	430
2020	304
2019	633
2018	345
2017	97
Prior	45
Revolving Loans Amortized Cost Basis	5
Total Loans	1,859
Consumer Non-real Estate [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	61
2020	94
2019	206
2018	56
2017	4
Prior	17
Revolving Loans Amortized Cost Basis	0
Total Loans	438
Oil and Gas [Member]
Financing Receivable Recorded Investment [Line Items]
2021	79,443
2020	1,021
2019	118
2018	59
Prior	0
Revolving Loans Amortized Cost Basis	37,803
Total Loans	118,444	179,355
Oil and Gas [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	56,060
2020	0
2019	54
2018	59
Prior	0
Revolving Loans Amortized Cost Basis	29,253
Total Loans	85,426
Oil and Gas [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	7,790
2020	1,021
2019	64
Revolving Loans Amortized Cost Basis	8,550
Total Loans	17,425
Oil and Gas [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	15,593
Total Loans	15,593
Other Loans [Member]
Financing Receivable Recorded Investment [Line Items]
2021	223,041
2020	32,392
2019	23,535
2018	16,755
2017	17,327
Prior	37,496
Revolving Loans Amortized Cost Basis	27,615
Total Loans	378,161	$ 822,078
Other Loans [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2021	223,041
2020	32,338
2019	23,410

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