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	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable Recorded Investment [Line Items]
2020	$ 2,637,796
2019	1,034,907
2018	618,426
2017	418,683
2016	327,103
Prior	598,412
Revolving Loans Amortized Cost Basis	759,179
Total Loans	6,394,506	$ 5,662,143
Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
Total Loans		4,462,594
Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
Total Loans		1,081,074
Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
Total Loans		96,850
Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Total Loans		21,344
Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
Total Loans		281
Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
2020	128,941
2019	93,608
2018	34,009
2017	42,392
2016	16,236
Prior	50,867
Revolving Loans Amortized Cost Basis	188,495
Total Loans	554,548	430,705
Pegasus Bank [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	100,631
2019	66,875
2018	27,235
2017	19,025
2016	12,414
Prior	44,237
Revolving Loans Amortized Cost Basis	113,824
Total Loans	384,241	295,243
Pegasus Bank [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	28,187
2019	26,733
2018	6,774
2017	23,367
2016	3,822
Prior	5,300
Revolving Loans Amortized Cost Basis	74,671
Total Loans	168,854	133,324
Pegasus Bank [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	123
Prior	1,330
Total Loans	1,453	1,287
Pegasus Bank [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
Total Loans		851
Real Estate [Member] \| Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
Total Loans	272,000
Real Estate [Member] \| Farmland [Member]
Financing Receivable Recorded Investment [Line Items]
2020	70,643
2019	57,379
2018	29,842
2017	21,563
2016	19,174
Prior	36,790
Revolving Loans Amortized Cost Basis	17,567
Total Loans	252,958	246,988
Real Estate [Member] \| Farmland [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	51,284
2019	26,391
2018	18,994
2017	13,821
2016	13,368
Prior	27,100
Revolving Loans Amortized Cost Basis	8,160
Total Loans	159,118
Real Estate [Member] \| Farmland [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	15,264
2019	30,684
2018	6,639
2017	6,391
2016	4,763
Prior	8,916
Revolving Loans Amortized Cost Basis	7,140
Total Loans	79,797
Real Estate [Member] \| Farmland [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	3,681
2019	290
2018	151
2017	1,055
2016	703
Prior	551
Revolving Loans Amortized Cost Basis	1,955
Total Loans	8,386
Real Estate [Member] \| Farmland [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	414
2019	14
2018	4,058
2017	296
2016	340
Prior	223
Revolving Loans Amortized Cost Basis	312
Total Loans	5,657
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
2020	189,212
2019	122,905
2018	86,436
2017	52,637
2016	51,923
Prior	117,021
Revolving Loans Amortized Cost Basis	21,853
Total Loans	641,987	621,188
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	142,574
2019	91,493
2018	73,845
2017	42,289
2016	37,097
Prior	88,724
Revolving Loans Amortized Cost Basis	17,153
Total Loans	493,175
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	42,375
2019	31,314
2018	11,516
2017	9,644
2016	13,316
Prior	25,574
Revolving Loans Amortized Cost Basis	4,393
Total Loans	138,132
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	4,226
2019	32
2018	333
2017	704
2016	1,259
Prior	2,671
Total Loans	9,225
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	37
2019	66
2018	742
2016	251
Prior	52
Revolving Loans Amortized Cost Basis	307
Total Loans	1,455
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Recorded Investment [Line Items]
2020	329,172
2019	209,503
2018	110,782
2017	89,871
2016	90,883
Prior	123,138
Revolving Loans Amortized Cost Basis	17,809
Total Loans	971,158	851,200
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	256,128
2019	157,526
2018	83,869
2017	69,864
2016	82,088
Prior	81,499
Revolving Loans Amortized Cost Basis	13,206
Total Loans	744,180
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	60,607
2019	48,751
2018	26,441
2017	18,070
2016	8,755
Prior	41,491
Revolving Loans Amortized Cost Basis	4,454
Total Loans	208,569
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	7,718
2019	3,137
2018	472
2017	1,937
2016	40
Prior	148
Revolving Loans Amortized Cost Basis	149
Total Loans	13,601
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	4,719
2019	89
Total Loans	4,808
Real Estate [Member] \| Construction and Development Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
2020	130,769
2019	66,435
2018	14,428
2017	5,368
2016	1,595
Prior	2,588
Revolving Loans Amortized Cost Basis	8,432
Total Loans	229,615	287,138
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	115,399
2019	56,369
2018	12,821
2017	4,582
2016	1,438
Prior	2,048
Revolving Loans Amortized Cost Basis	7,850
Total Loans	200,507
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	11,528
2019	10,002
2018	1,589
2017	764
2016	157
Prior	540
Revolving Loans Amortized Cost Basis	582
Total Loans	25,162
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	3,842
2018	9
Total Loans	3,851
Real Estate [Member] \| Construction and Development Less than 60 Months [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2019	64
2018	9
2017	22
Total Loans	95
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Recorded Investment [Line Items]
2020	188,716
2019	4,914
2018	181
2017	21
2016	33
Prior	491
Revolving Loans Amortized Cost Basis	11,839
Total Loans	206,195	189,480
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	159,431
2019	4,214
2018	69
2017	21
2016	33
Prior	23
Revolving Loans Amortized Cost Basis	11,449
Total Loans	175,240
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	27,400
2019	580
2018	112
Prior	468
Revolving Loans Amortized Cost Basis	390
Total Loans	28,950
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	1,885
2019	120
Total Loans	2,005
Real Estate [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable Recorded Investment [Line Items]
2020	273,560
2019	156,371
2018	104,388
2017	78,341
2016	63,501
Prior	177,155
Total Loans	853,316	834,849
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	241,771
2019	134,184
2018	80,793
2017	64,392
2016	48,686
Prior	136,059
Total Loans	705,885
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	28,305
2019	19,425
2018	21,742
2017	11,666
2016	12,365
Prior	34,312
Total Loans	127,815
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	2,754
2019	2,029
2018	1,375
2017	2,073
2016	1,213
Prior	5,194
Total Loans	14,638
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	730
2019	733
2018	478
2017	210
2016	1,186
Prior	1,590
Total Loans	4,927
Real Estate [Member] \| Residential Real Estate First Lien [Member] \| Grade 5 [Member]
Financing Receivable Recorded Investment [Line Items]
2016	51
Total Loans	51
Real Estate [Member] \| Residential Real Estate All Other [Member]
Financing Receivable Recorded Investment [Line Items]
2020	25,775
2019	16,297
2018	13,020
2017	8,255
2016	5,984
Prior	14,255
Revolving Loans Amortized Cost Basis	84,495
Total Loans	168,081	187,647
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	21,493
2019	13,944
2018	10,854
2017	6,265
2016	5,381
Prior	10,984
Revolving Loans Amortized Cost Basis	28,047
Total Loans	96,968
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	3,694
2019	1,675
2018	1,268
2017	1,809
2016	450
Prior	2,335
Revolving Loans Amortized Cost Basis	55,433
Total Loans	66,664
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	384
2019	461
2018	328
2017	116
2016	119
Prior	221
Revolving Loans Amortized Cost Basis	993
Total Loans	2,622
Real Estate [Member] \| Residential Real Estate All Other [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	204
2019	217
2018	570
2017	65
2016	34
Prior	715
Revolving Loans Amortized Cost Basis	22
Total Loans	1,827
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
2020	288,006
2019	174,031
2018	154,014
2017	82,315
2016	54,917
Prior	56,671
Revolving Loans Amortized Cost Basis	349,856
Total Loans	1,159,810	1,315,005
Commercial and Agricultural Non-Real Estate [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	206,515
2019	136,254
2018	124,657
2017	74,719
2016	46,453
Prior	33,471
Revolving Loans Amortized Cost Basis	270,426
Total Loans	892,495
Commercial and Agricultural Non-Real Estate [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	49,467
2019	34,659
2018	27,239
2017	6,566
2016	7,054
Prior	22,710
Revolving Loans Amortized Cost Basis	63,894
Total Loans	211,589
Commercial and Agricultural Non-Real Estate [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	24,793
2019	1,511
2018	1,466
2017	789
2016	271
Prior	327
Revolving Loans Amortized Cost Basis	14,577
Total Loans	43,734
Commercial and Agricultural Non-Real Estate [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	7,231
2019	1,607
2018	652
2017	241
2016	1,139
Prior	163
Revolving Loans Amortized Cost Basis	959
Total Loans	11,992
Consumer Non-real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
2020	180,241
2019	100,261
2018	45,442
2017	14,222
2016	5,092
Prior	2,137
Revolving Loans Amortized Cost Basis	8,010
Total Loans	355,405	359,529
Consumer Non-real Estate [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	166,934
2019	93,232
2018	41,449
2017	13,157
2016	4,471
Prior	1,768
Revolving Loans Amortized Cost Basis	7,673
Total Loans	328,684
Consumer Non-real Estate [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	12,773
2019	5,902
2018	3,399
2017	796
2016	499
Prior	266
Revolving Loans Amortized Cost Basis	328
Total Loans	23,963
Consumer Non-real Estate [Member] \| Grade 3 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	445
2019	840
2018	450
2017	175
2016	75
Prior	63
Revolving Loans Amortized Cost Basis	2
Total Loans	2,050
Consumer Non-real Estate [Member] \| Grade 4 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	89
2019	287
2018	144
2017	94
2016	47
Prior	40
Revolving Loans Amortized Cost Basis	7
Total Loans	708
Oil and Gas [Member]
Financing Receivable Recorded Investment [Line Items]
2020	147,335
2019	811
2018	82
Prior	4,679
Revolving Loans Amortized Cost Basis	26,448
Total Loans	179,355	184,399
Oil and Gas [Member] \| Grade 1 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	104,622
2019	66
2018	82
Prior	4,679
Revolving Loans Amortized Cost Basis	16,529
Total Loans	125,978
Oil and Gas [Member] \| Grade 2 [Member]
Financing Receivable Recorded Investment [Line Items]
2020	42,713

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